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Powder metallurgy (PM) commercial purity titanium (CP Ti) was fabricated and studied, with an aim of utilization for dental application. PM CP Ti was manufactured using a cost effective approach, where affordable hydrogenation–dehydrogenation (HDH) process Ti 99.4 wt.% powder was consolidated via the following sequence of PM techniques: cold isostatic pressing, warm vacuum pressing at 420 °C and warm direct extrusion at 500 °C. The paper presents the first studies on processing, microstructure, testing of mechanical properties, fatigue performance and bonding strength with different veneer coatings. By employed consolidation process sound material with low porosity (1.5%) and sustained oxygen content (0.21 wt.%) was attained. The tensile properties obtained for PM CP Ti (UTS = 701 MPa, YS 0.2 = 512 MPa, ε = 13 %) were improved over to those for cast / milled CP Ti Grade 4 reference, the material commonly used in dentistry. Tested using the ISO 14801 standard for dental implants, the samples machined from PM CP Ti showed fatigue performance similar to CP Ti Grade 4. PM CP Ti used as a metal base material in restoration metal – ceramic systems showed very good bond strength with three commercially available veneering ceramics and complied with the ISO 9693 standard. Within the limitations of this paper, the preliminary results demonstrated that performance of economic PM CP Ti is equal or superior to CP Ti Grade 4 reference material and it can be used in prosthodontics.
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CP Ti fabricated by low temperature extrusion of HDH powder:
application in dentistry.
Martin Balog1, a *, Josko Viskic2, b, Peter Krizik1, c, Zdravko Schauperl3, d,
Mateja Snajdar3, e, Zlatko Stanec4, f and Amir Catic2, g
1 Institute of materials and machine mechanics, Slovak academy of sciences, Racianska 75,
83102 Bratislava, Slovakia
2 School of Dental Medicine, University of Zagreb, Gunduliceva 5, 10 000 Zagreb, Croatia
3 Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lucica 5,
10000 Zagreb, Croatia
4 Private dental practice, Ljudevita Gaja 62a, 10430 Samobor, Croatia
a martin.balog@savba.sk, b viskic@sfzg.hr, c peter.krizik@savba.sk, d zdravko.schauperl@fsb.hr, e
mateja.snajdar@fsb.hr, f zlatko.mec@gmail.com, g catic@sfzg.hr
Keywords: dentistry, extrusion, mechanical properties, powder metallurgy, prosthodontic,
titanium, veneering
Abstract. Powder metallurgy (PM) commercial purity titanium (CP Ti) was fabricated and studied,
with an aim of utilization for dental application. PM CP Ti was manufactured using a cost effective
approach, where affordable hydrogenation–dehydrogenation (HDH) process Ti 99.4 wt.% powder
was consolidated via the following sequence of PM techniques: cold isostatic pressing, warm
vacuum pressing at 420 °C and warm direct extrusion at 500 °C. The paper presents the first studies
on processing, microstructure, testing of mechanical properties, fatigue performance and bonding
strength with different veneer coatings. By employed consolidation process sound material with low
porosity (1.5%) and sustained oxygen content (0.21 wt.%) was attained. The tensile properties
obtained for PM CP Ti (UTS = 701 MPa, YS0.2 = 512 MPa, ε = 13 %) were improved over to those
for cast / milled CP Ti Grade 4 reference, the material commonly used in dentistry. Tested using the
ISO 14801 standard for dental implants, the samples machined from PM CP Ti showed fatigue
performance similar to CP Ti Grade 4. PM CP Ti used as a metal base material in restoration metal
ceramic systems showed very good bond strength with three commercially available veneering
ceramics and complied with the ISO 9693 standard. Within the limitations of this paper, the
preliminary results demonstrated that performance of economic PM CP Ti is equal or superior to CP
Ti Grade 4 reference material and it can be used in prosthodontics.
Introduction
Practical use of Ti is motivated by its extraordinary chemical resistance, excellent damage tolerance
and low density. Since the beginning of industrial production of Ti, focus of its use has been in
space technology, military aircrafts and chemical industry [1]. Furthermore, Ti has been used for
equipment operating in seawater, surgical instruments, in luxury watches and jewelry [1]. Metallic
Ti, despite its high content in the earth's crust, is considered to be rare and expensive material [2].
The reason is that the conventional metallurgical methods are ineffective in case of Ti due to the
high reactivity of Ti at elevated temperatures with a wide range of elements [3]. Because of the
problematic and expensive casting in controlled atmosphere of inert gasses, Ti semi-products are
machined, which results in a great loss of expensive material [4]. However, machining of Ti
(especially CP Ti) by conventional machining methods has other disadvantages such as high cutting
temperature and high tool wear ratio [5]. As a result, CP Ti is classified as difficult-to-machine
material. For these reasons there is growing interest in PM as a cost-effective approach of direct
production of complex Ti parts [6]. Additionally, PM approach brings benefits in significantly
improved chemical and microstructural homogeneity of components and possibility to produce
various composite structures [7]. PM Ti parts may be fabricated by a wide range of techniques,
where press-and-sinter approach is technically most simple and economically most attractive
approach capable of production of near-to-shape parts. However, limiting fact is that the sintering
has to be realized under relatively high vacuum by batch type process, which restricts effectiveness
and reproducibility, in addition to relatively high residual porosity, which predetermines
applications under non fatigue conditions [8].
Recognized for excellent biocompatibility, corrosion resistance, low density and good mechanical
properties, CP Ti is widely employed as implant and prosthodontic material in orthopedics and
dentistry [9]. In case of patient’s intolerance to other common dental metallic materials, such as
cobalt-chrome (Co-Cr) alloys, CP Ti is often used as substitute base metal for dental prosthodontic
products (e.g., crowns and bridges). Low density of CP Ti becomes of importance for large and
heavy prosthodontic products. Notwithstanding these positive qualities, the α-Ti β-Ti phase
transformation leads to formation of a thick oxide surface layer. However, an optimum firing
temperature, at which common dental veneering porcelains are applied to a base material for
restoration by metal - ceramic system, is above the α-Ti β-Ti phase transformation temperature.
This restricts formation of strong bonds between veneering porcelains and CP Ti used as a base
material [10]. Moreover, the mechanical strength of CP Ti is relatively low; in addition to high cost
of cast CP Ti blanks, that are used for CNC milling of prosthodontic products (e.g., crowns and
bridges) [11]. To overcome these limitations, in this study high performance PM CP Ti material was
fabricated by novel economic PM approach. Herein, consolidation was realized by hot working of
HDH Ti powders at relatively low processing temperatures (< 500 °C). At used processing
temperatures CP Ti becomes relatively easy-to-deform, while the problems associated with high
reactivity of CP Ti in contact with the used tooling and the atmosphere are avoided. Comparison of
studied PM CP Ti to CP Ti Grade 4 reference, the common material of dental prosthodontics and
implants, was made. Following international standards the mechanical properties and bonding
strength of PM CP Ti with various veneering ceramics was assessed. In order to consider
detrimental effect of residual porosity on fatigue performance, PM CP Ti underwent rigorous
fatigue testing standardized for dental implants.
Experimental
HDH CP Ti (99.4 wt.%) powder (Kimet, China) with the median particle size d50 = 84.5 µm (< 150
µm fraction) and oxygen content 0.21 ± 0.01 wt.% was used in this study (Fig. 1). Alternatively
finer fraction (< 31 µm) of HDH CP Ti powder with oxygen content 0.54 ± 0.03 wt.% was used for
comparison. FRITSCH Analysette 22 laser diffraction system was used to determine powder
particle size distribution. By LECO OHN836 analyzer oxygen content on loose powder and
compacts was determined. Simultaneous DSC-TGA measurements were conducted in air using
Q600 TA Instruments machine. Loose powder was cold compacted by cold isostatic pressing (CIP)
at 200 MPa. CIP blanks were compressed by uniaxial vacuum pressing (VP) at 420 °C and 425
MPa. VP blanks were consolidated by direct extrusion (DE) at 500 °C to final profiles either with
the diameter of 6 mm (the reduction ratio of R = 11:1) or the cross-sections of 13 × 13 mm2 (R =
4:1). The materials extruded from Ti <150 µm and <31 µm powders were labeled as PM CP Ti
(<150 µm) and PM CP Ti (<31 µm), respectively.
The density of the prepared samples was measured using the Archimedes’ principle according to the
ASTM B962-08 standard. The microstructures were characterized using light microscope (LM,
Olympus GX51) and scanning electron microscope (SEM, JEOL 7500 machine) equipped with
energy dispersive X-ray spectrometer (EDS) and X-ray diffraction (XRD, Philips PW 1830
diffractometer). Tensile specimens with 3 mm diameter and 30 mm gauge length were machined
along the longitudinal direction of the extruded materials with the diameter of 6 mm. The specimens
were tested using a Zwick Roell 1474 machine at a strain rate of ~5·10-4 s-1 according to the ASTM
E8 and ASTM E21 standards. The Young`s modulus (E) was measured by dynamic mechanical
analysis (DMA, TAQ800 machine) using 5 × 2.5 × 55 mm3 bars and the three-point bending
method. Fatigue testing of dental implant shaped specimens, machined from PM CP Ti (<150 µm)
extruded profiles with the diameter of 6 mm, was conducted to follow the ISO 14801 standard [12].
The implants with the diameter of 3.8 mm and the length of 9.5 mm were mounted in a supporting
PMMA resin structure at an angle of 60° with the horizontal. An alternating load was applied
vertically through the center of the hemisphere on the end of the implant. The load introduced to
inclined implant results in a bending that generates a zone of tensile stresses. The load was adjusted
to vary following a sinusoidal pattern with the frequency of 15 Hz and 5·106 cycles, such that the
minimum load represented 10% of the maximum load.
Three commercially available veneering ceramics: i. GC Initial Ti; ii. DeguDent Duceratin Kiss; and
iii. Vita Titankeramik, used for commercially available cast / milled CP Ti were applied on PM CP
Ti (<150 µm). The samples with dimensions (25 ± 1) × (3 ± 0.1) × (0.5 ± 0.05) mm3 were machined
from PM CP Ti (<150 µm) extruded profiles with 13 × 13 mm cross-section by wire electro
discharge machining (WEDM). The machined samples were mechanically grinded to remove the
surface affected by WEDM (i.e., Cu and O contaminants), which affects veneering process and
bond strength [14]. WEDMed samples were divided into 4 groups according to the surface
modifications: i. untreated; ii. sandblasted (by Al2O3); iii. applied bonding agent; iv. sandblasted
(Al2O3) and applied bonding agent. Each group was divided into 3 subgroups of 8 samples and
veneering ceramics was applied. Veneering ceramics were applied by fusion processes
recommended by manufacturers at the peak firing temperature of 760 °C (Initial Ti), 810 °C
(Duceratin Kiss) and 800 °C (Titankeramik). The three point bending test according to the ISO 9693
was used to determine bonding strength of PM CP Ti (<150 µm) specimens with the veneering
ceramics applied [13].
Fig. 1 SEM image of as-received Ti <150 µm (a) and <31 µm (b) powders.
Results and discussion
Simultaneous DSC-TGA measurements performed on as-received Ti <150 µm loose powder in air
indicate the onset of oxidation at ~550 °C (Fig. 2). For this reason the maximum processing
temperature, at which detrimental oxidation is avoided, was limited to 500 °C. In spite of the results
obtained from DSC-TGA analyses, an introduction of VP technological step prior DE was necessary
in order to maintain oxygen content. Simplified process of DE of green powder compacts (Ti <150
a
b
µm powder) cold compacted by CIP resulted in slight increase of oxygen content to 0.24 ± 0.01
wt.%. On the contrary, the oxygen content remained unchanged (0.21 ± 0.01 wt.%) compared to as-
received loose powder after DE of precompacts cold / warm compacted by CIP / VP (Table 1). The
oxygen level determined in PM CP Ti (<150 µm) is within the ASTM B265 and B988 limit (<0.4
wt.%) defined for cast Ti Grade 4 and Ti Grade 4 PM, respectively. The breakthrough pressures
determined during laboratory scale DE consolidation (Ti <150 µm powder, at 500 °C) were at the
level of ~500 and ~1400 MPa for R = 4:1 and 11:1, respectively. A negative contribution of friction
forces on the wall of small diameter container to total extrusion force is relatively large at laboratory
scale. The pressure limit of industrial extrusion presses with larger diameter containers is typically
at ~900 MPa. Thus, a future up-scaling of applied consolidation process is feasible if DE is realized
at low to medium R. DE yielded sound profile materials with 99.9 ± 0.1% of the theoretical density
(THD = 4.506 g.cm-3). A relatively high density determined by the Archimedes’ principle was in
agreement with a small porosity of cross sectional microstructures observed by LM (Fig. 3a). The
microstructure of extruded material in longitudinal direction is characterized by mixture of the
grains elongated along extrusion direction and equiaxed grains with the size of ~1 µm (Fig. 3b).
Good metallurgical bonding free of voids and pores was created at Ti powder interfaces. The tensile
tests revealed good reproducibility of obtained mechanical properties of extruded PM CP Ti (<150
µm), as shown in Fig. 4. PM CP Ti (<150 µm) showed relatively high offset yield strength YS0.2 =
512 ± 11 MPa and ultimate tensile strength UTS = 701 ± 4 MPa, accompanied with reasonably high
true elongation 13 ± 2% and E = 99 ± 0.5 GPa (Tab. 1). The tensile strengths of PM CP Ti (<150
µm) improved significantly over the standardized strengths for cast Ti Grade 4 and Ti Grade 4
PM100. The mechanical properties stem from the fine grain size (i.e., powder particle size) and are
comparable to severely deformed ultrafine-grained CP Ti (e.g., four equal channel angular pressing
(ECAP) passes) [12, 15]. On expense of the high strengths, elongation of extruded PM CP Ti (<150
µm) was slightly below the limits defined by ASTM B265 (15%) and B988 (18%). Due to the finer
grain size and increased oxygen content (0.54 ± 0.03 wt.%) the strengths significantly increase and
true elongation decreases for PM CP Ti material extruded from the finer (<31 µm) powder.
However, laboratory scale DE of the finer powder yielded extremely high breakthrough pressures
(~700 and ~1700 MPa for R = 4:1 and 11:1, respectively), what makes extrusion compaction of this
powder difficult to implement at industrial scale. For this reason the later development in this study
focuses only on PM CP Ti (<150 µm). Tensile tests confirmed detrimental effect of oxygen picked
up during consolidation processing. PM CP Ti (<150 µm) extruded from green powder compacts
cold compacted by CIP without applied VP showed similar strengths (YS0.2 = 511 ± 14 MPa and
UTS = 698 ± 1 MPa), but significantly lower elongation = 7 ± 1%) compare to the material
extruded from CIP / VP precompacts. This suggests that additional oxidation of powder during
heating prior DE leads to thickening of powder surface TiO2 layers, what deteriorates an effective
metallurgical bonding on Ti powder interfaces and reduces elongation of extruded material,
eventually. Furthermore, application of VP step minimizes a residual porosity of extruded materials.
PM CP Ti (<150 µm) extruded directly from CIP powder shows higher porosity (99.5 ± 0.1% of
THD), what results in further decrease of elongation.
Fig. 2 Simultaneous DSC-TGA curves of as-received Ti <150 µm powder during heating in air.
Fig. 3 LM (a) and TEM (b) micrographs of extruded PM CP Ti (<150 µm) shown in longitudinal
direction.
a
b
Fig. 4 The tensile stress-strain curves of PM CP Ti (<150 µm) and PM CP Ti (<31 µm).
Table 1 The mechanical properties of PM CP Ti (<150 µm) and PM CP Ti (<31 µm).
YS0.2 – offset yield strength, UTS – ultimate tensile strength and ε – the true elongation (obtained
from the tensile tests), and E – Young`s modulus (obtained from DMA).
Powder size
(µm)
Oxygen content
(wt.%)
YS
0.2
(MPa)
UTS
(MPa)
ε
(%)
E
(GPa)
< 150
0.21 ± 0.01
512 ± 11
701 ± 4
13 ± 2
99 ± 0.5
< 31
0.54 ± 0.03
768 ± 20
1024 ± 27
6 ± 1
100 ± 0.1
It is widely believed that PM products suffer from poor fatigue life performance. For this reason, the
fatigue testing of 3.8 × 9.5 mm specimens machined from CP Ti (<150 µm) profile was carried out
in conformity with the ISO14801 standard for dental implants (Fig. 5a). Nevertheless, real-life
fatigue straining of dental implants is significantly more pronounced compare to dental
prosthodontic products (e.g., crowns and bridges). Thus fatigue testing of CP Ti (<150 µm) as a
base metal for prosthodontic parts according to the ISO14801 standard is rather rigorous. The tests
revealed that the maximum tested load, which specimens endured at 5·106 cycles, was 400 N. As
earlier works reported, the ratio between fatigue limit and static strengths of CP Ti Grade 1-4
remains relatively constant independently to interstitial content and grain size (i.e., cold working)
[16, 17]. This represents the fatigue limits / yield strength ratio of ~0.78, that is higher than the ratio
of ~0.65 reported for CP Ti in [16]. Furthermore, it was known that similarly to the static strengths
the endurance limit of CP Ti increases with increasing oxygen content [18]. The oxygen content
(0.21 wt.%) of PM CP Ti (<150 µm) was distinctly below the ASM limit defined for CP Ti Grade 3
(<0.35 wt.%) and Grade 4 (<0.4 wt.%). Still the fatigue limits obtained for PM CP Ti (<150 µm)
were higher than the fatigue limits of ~300 N reported for CP Ti Grade 3 implants (3.8 × 10 mm)
[19], and were at the level of the fatigue limits (~420 N) reported for the larger size CP Ti Grade 4
implants (4.1 × 12 mm) [20]. Thus, in spite of present porosity and low oxygen content, dental
implants fabricated of PM CP Ti (<150 µm) had the capability of withstanding fatigue limits similar
to cast and milled CP Ti Grade 4 reference.
Table 2 summarizes the bond strengths of the veneering ceramics applied on PM CP Ti (<150 µm)
substrate. For Initial Ti and Titankeramik ceramics the highest values of bond strength were
obtained for specimens that were only sandblasted and for Duceratin Kiss the specimens that were
sandblasted and then treated with a bonding agent. As indicated by Pearson correlation coefficient
between the surface roughness and the bond strength values (r2–35 % for Duceratin Kiss, r260 %
for Initial Ti and r282 % for Titankeramik) the bond strength increases due to roughening of
substrate surface by surface treatment (i.e., namely sandblasting). Surface of sandblasted samples
showed significantly higher roughness parameters (Ra, Rz and Rmax). Untreated specimens or the
specimens treated with a bonding agent without sandblasting showed lower bond strength. The
bonding agent, recommended by manufacturer, differs for each ceramic used. It seems that
Duceratin Kiss bonding agent plays a more significant role in creating a better connection than the
other two. According to the manufacturers’ recommendation, the proper surface treatment of cast /
milled CP Ti substrate before veneering for all three applied ceramics is first sandblasting and then
applying the respective bonding agent. However, the results for PM CP Ti (<150 µm) showed that
the bond strength for Initial Ti and Titankeramik ceramics is increased if the surface is treated only
by sandblasting without addition of bonding agent. The SEM, EDS and XRD analyses of samples
showed predominantly adhesive fractures between veneering ceramics and metal samples. The
maximum bond strength for PM CP Ti (<150 µm) with Initial Ti, Duceratin Kiss and Titankeramik
ceramics applied was 38.5, 41.2 and 38.5 MPa, respectively. These values are higher than 25 MPa,
which is the minimum requirement for bond strength defined by the ISO 9693 standard. The bond
strength of cast and milled CP Ti Grade 4 varies typically between 21 45 MPa [21, 22]. Fig. 5b
shows the crown`s metal base parts, which were successfully CNC machined from extruded PM CP
Ti (<150 µm).
Table 2 The bond strengths of three veneering ceramics applied on PM CP Ti (<150 µm) substrate
with the different surface treatment.
Veneering ceramic
Surface treatment
Bond strength
(MPa)
Initial Ti
untreated
12.7 ± 1.3
sandblasted
38.5 ± 2.7
bonding agent
25.3 ± 2.1
sandblasted + bonding agent
31.6 ± 1.8
Duceratin Kiss
untreated
34.3 ± 6.3
sandblasted
33.4 ± 2.8
bonding agent
30.2 ± 2.8
sandblasted + bonding agent
41.2 ± 1.2
Titankeramik
untreated
17.3 ± 4.5
sandblasted
38.5 ± 1.4
bonding agent
22.3 ± 2.4
sandblasted + bonding agent
32.3 ± 1.7
b
a
Fig. 5 Fatigue testing set up: implant shaped specimen embedded in a supporting PMMA resin
structure (a) and CNC machined dental crowns (b) fabricated from PM CP Ti (<150 µm).
Conclusions
PM CP Ti was manufactured by consolidation of affordable HDH Ti 99.4 wt.% powders (<150 and
<31 µm fractions) by warm vacuum pressing and direct extrusion at temperatures < 500 °C.
Extruded PM CP Ti was assessed from perspective of application in dentistry as prosthodontic
material. Within the limitations of this study, the following conclusions can be made:
Employed consolidation process yielded sound material with low porosity and sustained oxygen
content. Introduction of vacuum pressing step was necessary in order to maintain oxygen
content in extruded material unchanged compared to as-received powder.
Extrusion of coarser Ti powder (<150 µm fraction) at laboratory scale resulted in acceptable
breakthrough pressures, that predetermines future up-scaling possible. On the contrary,
extrusion of finer Ti powder (<31 µm) yielded extremely high breakthrough pressures, that
makes manufacturing difficult to implement at industrial scale.
PM CP Ti (<150 µm) showed high strengths UTS = 701 MPa, YS0.2 = 512 MPa and reasonable
ε = 13 %. The tensile strengths of PM CP Ti (<150 µm) were improved over to those for CP Ti
Grade 4, the reference material widely employed in dentistry.
Fatigue life of implant shaped specimens machined from PM CP Ti (<150 µm) tested in
compliance with the rigorous standard for dental implants, and is comparable to CP Ti Grade 4.
PM CP Ti (<150 µm) used as a metal base material in restorative metal ceramic systems
showed very good bond strength with three commercially available veneering ceramics. The
bond strengths were comparable with those obtained for commercial cast / milled CP Ti Grade
4. PM CP Ti (<150 µm) conformed to the ISO 9693 standard and can be used in prosthodontics
as a metal base material.
Because of a cost effective approach used in this study, manufactured PM CP Ti (<150 µm)
material is relatively cheap and near net shape extruded products are suited for (CNC)
machining of prosthodontic products and dental implants.
Acknowledgments
Financial support from the SRDA APVV-0556-12 project, the VEGA 2/0065/16 and 2/0025/14
projects, the ITMS 26240220088 and 26240120020 projects, and MESS No. 065-0650446-0435
University support „Research of new ceramic materials and technologies in dental prosthodontics"
is gratefully acknowledged. The authors thank Peter Svec of IPSAS for help with TEM
characterization.
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... The graphite flakes of average particle size of 16 µm with aspect ratio of flakes 10 (diameter to thickness ratio) and purity 99.9% are shown in Figure 1b. The powder was compacted using cold isostatic pressing followed by hot vacuum pressing at the temperature of 450 • C and pressure of 500 MPa [57]. The density of samples was determined from weighting and volume measurement to be in the range of 4.1-4.15 ...
... The graphite flakes of average particle size of 16 µm with aspect ratio of flakes 10 (diameter to thickness ratio) and purity 99.9% are shown in Figure 1b. The powder was compacted using cold isostatic pressing followed by hot vacuum pressing at the temperature of 450 °C and pressure of 500 MPa [57]. The density of samples was determined from weighting and volume measurement to be in the range of 4.1-4.15 ...
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... In this work, in order to develop a low elastic modulus alloy for biomedical applications, a new type of bimetallic Ti-Mg composite [18] , named BIACOM (bioactive composite metal) [19] , possessing both bioinert and biodegradable characteristics has been proposed and manufactured through the use of PM warm powder consolidation process. This study, which is a continuation of preliminary work, focused on describing the technology and optimizing the parameters for production of Ti-Mg composite. ...
... Fig. 3 shows the tensile stress-strain curves of both as-extruded coarse (d 50 =76 μm) and fine (d 50 =26 μm) Ti alloy at high reduction ratio. The tensile tests revealed good reproducibility of obtained mechanical properties of extruded PM coarse Ti which, showed relatively high offset yield strength YS 0.2 = 411 ± 1 MPa and ultimate tensile strength UTS = 598 ± 3 MPa, accompanied with high elongation 31.3% ± 1.8 % and E = 99.7 ± 0.2 GPa ( Table 3) that are compatible with the standardized strengths for cast Ti Grade 4 and Ti Grade 4 PM100 and are in the same line with previous results reported in [19]. Due to the finer grain size and increased oxygen content (0.576 ± 0.004wt.%), ...
Conference Paper
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The paper introduces titanium-magnesium (Ti-Mg) composite manufactured by warm consolidation powder metallurgy (PM) approach to be used as a dental implant. Composite structure consists of bioinert Ti matrix, which provides mechanical properties after implantation process, and biodegradable Mg component, which has a dual role: (1) it decreases the Young`s modulus (E) and (2) it selectively elutes from surface and volume of implant after implantation, and leaves pores on a prior location, which act as sites for new bone ingrowth. That leads to an improvement of existing material concepts of dental implants based on commercial purity (CP) Ti and TiAl6V4, which suffer from stress-shielding effect and insufficient implant`s surface bioactivity. In this study, a performance of Ti-Mg composite was optimized as a function of Mg component, extending from 0 to 24 vol. %, and particle size fraction of Ti powder at different extrusion ratio. The microstructure and mechanical properties of as-extruded composites were characterized by scanning electron microscopy (SEM) equipped by energy dispersive spectrometry (EDS), tensile mechanical testing and dynamic mechanical analysis (DMA). The results obtained for Ti-Mg composite extruded at high reduction ratio showed homogenous structure in which, Ti matrix is embedded with Mg and both are in direct contact at the interfaces without any pores, voids or increased oxygen (O) content. The composites with 24 vol.% Mg reached E = 81 GPa, yield strength of 340 MPa, ultimate tensile strength of 409 MPa and ductility of 1.1 %, which are adequate values for endosseous dental implant application.
... The development of the radio frequency plasma (RF) technique provides a powerful tool to reduce the costs of spherical metal powders [13]. This approach has been intensively researched for the manufacturing of cost-effective titanium spherical powders using low-cost hydrogenated-dehydrogenated (HDH) titanium powder [14]. Combining the advantages of the manufacturing capacity of AM technology and spherical HDH titanium powder with RF treatment, in this study, AM-HDH-RFproduced Ti components achieved superior mechanical properties and were prepared at a low-cost compared to those prepared using traditional processing techniques [15]. ...
Article
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Titanium for additive manufacturing presents a challenge in the control of costs in the fabrication of products with expanding applications compared with cast titanium. In this study, hydrogenated–dehydrogenated (HDH) titanium powder with a low cost was employed to produce spherical Ti powder using the radiofrequency plasma (RF) technique. The spherical Ti powder was used as the raw material for laser directed energy deposition (LDED) to produce commercially pure titanium (CP-Ti). Microstructural analyses of the powder revealed that RF treatment, not only optimized the shape of the titanium powder, but also benefited in the removal of the residual hydride phase of the powder. Furthermore, the LDED-HDH-RF-produced samples showed an excellent combination of tensile strength and tensile ductility compared to the cast and the LDED-HDH-produced samples. Such an enhancement in the mechanical properties was attributed to the refinement of the α grain size and the dense microstructure. The present work provides an approach for LDED-produced CP-Ti to address the economic and mechanical properties of the materials, while also providing insights into the expanding application of HDH titanium powder.
... The press-and-sinter approach is economically the most attractive approach to the production of near-to-shape parts, but it results in a relatively high residual porosity [29]. By contrast, CP Ti, fabricated by an economic PM approach realized by the warm extrusion of a Ti powder, showed mechanical properties and fatigue life superior to the Ti Grade 4 reference material, which is commonly used in dentistry for prosthodontics parts and implants [30]. This motivated the idea to produce a two-phase Ti + Mg material that would selectively exploit the advantages of both biometals. ...
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Metallic implant materials are biomaterials that have experienced major development over the last fifty years, yet some demands posed to them have not been addressed. For the osseointegration process and the outcome of endosseous implantation, it is crucial to reduce the stress shielding effect and achieve sufficient biocompatibility. Powder metallurgy (PM) was utilized in this study to fabricate a new type of titanium (Ti) + magnesium (Mg) bioactive composite to enable stress-shielding reduction and obtain better biocompatibility compared with that of the traditional Ti and Ti alloys used for dental implants. Such composites are produced by well-known cost-effective and widely used PM methods, which eliminate the need for complex and costly Ti casting used in traditional implant production. The relation between the microstructure and mechanical properties of as-extruded Ti + (0 - 24) vol.% Mg composites was investigated with respect to the Mg content. The microstructure of the composites consisted of a biodegradable Mg component in the form of filaments, elongated along the direction of extrusion, which were embedded within a permanent, bioinert Ti matrix. As the Mg content was increased, the discrete filaments became interconnected with each other and formed a continuous Mg network. Young`s modulus (E) of the composites was reduced to 81 GPa, while other tensile mechanical properties were maintained at the values required for a dental implant material. The corrosion behavior of the Ti + Mg composites was studied during immersion in a Hank's balanced salt solution (HBSS) for up to 21 days. The elution of Mg pores formed at former Mg sites led to a further decrease of E to 74 GPa. The studied compositions showed that a new Ti + Mg metallic composite should be promising for load-bearing applications in endosseous dental implants in the future.
Conference Paper
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The field of biocompatible material surfaces is a widely researched topic. Surface energy, surface topography and surface chemistry are important properties of biocompatible surfaces. These properties contribute to better osseointegration and adhesion of cells to implant surfaces. This article investigates the chemical and phase composition of the surface of a new titanium composite produced by powder metallurgy. Surface oxidation of the graphite-titanium metal matrix composite (TiMMC) after laser beam micromachining (LBMM) is discussed in this paper. Laser micromachining was performed in an argon shielding atmosphere and air. The aim was to determine the influence of the shielding atmosphere and the input parameters of LBMM on the presence of oxygen on the surface. Laser-treated surfaces were examined with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The phase composition was analysed with X-ray diffraction (XRD). Experiments confirmed that an argon shielding atmosphere reduces surface oxidation. The oxidation was also affected by the energy of the laser beam acting on the material. The maximum amount of oxygen detected on the surface after LBMM in air and argon was 38.6 wt. % and 24.2 wt. %, respectively. The presence of TiO, TiO2 and Ti2O3 oxides were detected on the surface after laser ablation in air. In contrast, Ti2O3 and TiO oxides were detected after laser ablation in the argon shielding atmosphere.
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The applicability of concentrated solar power for metallurgy of titanium is discussed based on preliminary experimental works performed at Plataforma Solar de Almeria Spain, using solar furnace SF40 under protective argon atmosphere. As a starting material, titanium powder was used. The possibility of melting titanium compacts on yttria stabilized zirconia mat was investigated, and the effect of density and size of different green compacts was studied. It was observed that the time to achieve melting point is very short when concentrated solar power is used. The obtained results are expected to be similar for titanium sponge from which titanium powder is processed. After optimization of processing parameters, this will probably lead to a significant decrease of carbon footprint in the titanium ingots and castings production.
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We report on the study on the titanium-magnesium (Ti–Mg) bioactive metal-metal composite utilized for a fabrication of dental implants. The biomedical Ti-12vol.%Mg composite, named BIACOM, is manufactured using a cost effective approach, where a mixture of elemental Ti and Mg powders is extruded at low temperature to sound profiles. Microstructure of composite comprises filaments of biodegradable Mg component, which are arrayed along extrusion direction and are homogenously distributed within permanent, bioinert Ti matrix. Compared to Ti Grade 4, the reference material used for dental implants, the properties of as-extruded composite include significantly reduced Young’s elastic modulus (92.1 GPa) and low density (4.12 g.cm−3), while the mechanical strength of Ti Grade 4 is maintained. Dynamic testing of dental implants fabricated from as-extruded composite, realized to follow the ISO 14801 standard for endosseous dental implants, confirms fatigue performance of BIACOM implants equal to the one of the reference material. Exposure of as-extruded composite samples to Hank’s solution, realized in order to simulate behavior in human body over the time after implantation, yields gradual dilution of Mg from composites surface and volume. Corroded Mg leaves at prior Mg filament sites pores within Ti matrix, which remains intact. This provides further decrease of Young’s modulus and enhances macro and micro roughness at implants surface. As a result, BIACOM shows improved mechanical compatibility (i.e., reduction of stress-shielding) and better osseointegration potential.
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The brand new technology for sintering of titanium was tested: For the first time, titanium powder was pressure less sintered under argon atmosphere at different temperatures and time, in 5 kW vertical axis solar furnace at Plataforma Solar de Almeria (PSA), Spain. The decrease of final porosity with increasing sintering temperature and time at constant heating rate is observed. The obtained results are compared with those obtained for identical green powder compacts sintered in vacuum furnace. Final porosity below 5% was achieved and shorter sintering times were observed. Radial shrinkage of samples at solar furnace is almost the same as at vacuum furnace. On the contrary axial shrinkage is 20% higher. It was proposed that this can be attributed to argon gas used during sintering and due to the different heating in solar furnace during sintering. Argon at lower temperature acts as a heat transfer medium and helps to distribute the heat more homogeneously into the powder compacts. At higher temperature it remains enclosed in the pores thereby increasing a bit final compact porosity when compared with vacuum furnace. It was further showed that the contents of O, N, H in final compacts depend predominantly on their concentration in original powder. The observed increase due to technology is 300 ppm for oxygen and 80 ppm for nitrogen. Hydrogen concentration decreased significantly. Microhardness dependence on porosity of prepared samples was also investigated and microhardness of bulk Ti prepared in solar furnace was estimated to be 282.2 ± 28.3 HV0.5.
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Titanium and its alloys are attractive materials due to their unique high strength-weight ratio that is maintained at elevated temperatures and their exceptional corrosion resistance. The major application of titanium has been in the aerospace industry. However, the focus shift of market trends from military to commercial and aerospace to industry has also been reported. On the Other hand, titanium and its alloys are notorious for their poor thermal properties and are classified as difficult-to-machine materials. These properties limit the use of these materials especially in the commercial markets where cost is much more of a factor than in aerospace. Machining is an important manufacturing process because it is almost always involved if precision is required and is the most cost effective process for small volume production. This paper reviews the machining of titanium and its alloys and proposes potential research issues.
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Titanium-ceramic bonding is an unsolved problem for the current use of titanium-ceramic restorations. The purpose of the study was to characterize oxide formation on titanium surfaces at porcelain sintering temperatures and to determine the effect of chromium coating methods on titanium oxide formation. Sputter coating and electroplating methods of chromium application were compared and combined. Porous, weak titanium oxide formation on uncoated samples was demonstrated at porcelain sintering temperatures. Groups with chromium coating as an oxygen diffusion barrier exhibited lower oxidation rates, except samples coated by sputtering alone. Temperature effect was found to have the greatest significance on titanium oxidation rate. The overall lowest oxidation rate was located in the group that had chromium coating by the combined coating method and was oxidized at 750 degrees C. The electroplating method requires further investigation and development so that a uniform chromium layer can be deposited on titanium.
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