ArticlePDF Available

Microstructural investigation of as cast and PREP atomised Ti-6Al-4V alloy


Abstract and Figures

A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V powders from an alloy electrode. The process parameters and their impact on the material properties are described. The effects of electrode rotation speed on the particle size distribution, particle shape and crystal structure are investigated in detail. Optical microscopy and scanning electron microscopy are used for microstructural characterisation. The analysis shows that cast and extruded Ti–6Al–4V alloys have equiaxial a and azb phase structures, while plasma rotating electrode processed powder from the same alloy compositions has an acicular or martensitic (a) structure. The microstructure scale depends on the particle size. Microhardness measurements are used to assess mechanical property dependence on the microstructure of this alloy. The rapidly cooled alloy particles have much higher hardness than cast or extruded bulk alloy.
Content may be subject to copyright.
Microstructural investigation of as cast and
PREP atomised Ti–6Al–4V alloy
R. Yamanoglu*
, R. M. German
, S. Karagoz
, W. L. Bradbury
, M. Zeren
W. Li
and E. A. Olevsky
A microstructure characterisation of Ti–6Al–4V is conducted for cast, extruded and micrometre
sized particles. The plasma rotating electrode process is used to produce spherical Ti–6Al–4V
powders from an alloy electrode. The process parameters and their impact on the material
properties are described. The effects of electrode rotation speed on the particle size distribution,
particle shape and crystal structure are investigated in detail. Optical microscopy and scanning
electron microscopy are used for microstructural characterisation. The analysis shows that cast
and extruded Ti–6Al–4V alloys have equiaxial aand azbphase structures, while plasma rotating
electrode processed powder from the same alloy compositions has an acicular or martensitic (a)
structure. The microstructure scale depends on the particle size. Microhardness measurements
are used to assess mechanical property dependence on the microstructure of this alloy. The
rapidly cooled alloy particles have much higher hardness than cast or extruded bulk alloy.
Keywords: Solidification, Microstructural characterisation, Ti–6Al–4V powders, PREP atomisation
Titanium and its alloys have been under active research
for the past 50 years. Titanium alloys have many
advantages, such as high strength/weight ratio, excellent
corrosion resistance and biocompatibility.
forging and powder metallurgy are established techni-
ques for processing titanium. A variety of advanced
techniques have emerged in recent years: electron beam
melting, laser engineered net shaping, direct metal
laser sintering and ultrasonic consolidation; however,
wrought products continue to dominate titanium usage.
Powder metallurgy offers an alternative route which has
demonstrated significant gains in material utilisation
and faster conversion into final products.
Ti–6Al–4V is the most widely used titanium alloy for
industrial applications. Prior research has reported that
the mechanical properties of titanium are strongly
dependent on porosity, impurity content and pore size.
Consequently, proper processing of alloy powders enables
production of low porosity materials with uniform pore
size, or even full density with desired mechanical proper-
ties, comparable to wrought materials.
Pure titanium and Ti–6Al–4V have shown promise as
biomedical implant components.
Commercially pure
titanium, Ti–6Al–4V and extra low interstitial Ti–6Al–4V
can be also used for many structural applications, such as
in the aerospace industry.
The plasma rotating electrode process (PREP) is a
useful technique to produce rapidly solidified spherical
Ti based alloy powders with low impurity levels.
In the
present study, the microstructures and morphologies
of the alloy powders produced by the PREP were
investigated in detail by means of optical microscopy
and scanning electron microscopy (SEM). The effects of
the rotation speed on the particle size and material
properties are discussed.
The chemical composition of the titanium alloy Ti–6Al–
4V used in this study is 89?45Ti–6?20Al–4?14V–0?02Si–
0?01Mn–0?14Fe–0?04Nb (wt-%). Aluminum additions
stabilise the hexagonal close packed aphase, and
vanadium, being body centreed cubic, stabilises the b
phase. When Ti–6Al–4V is slowly cooled from the b
temperature, aphase regions begin to form below the
btransus temperature which is y980uC. The kinetics of
bRatransformation during cooling strongly influences
resulting properties of this alloy.
Potential areas of
application for titanium and its alloys depend strongly
on their phase structure.
Plasma rotating electrode process atomisation
To produce Ti–6Al–4V alloy powders, cast and extruded
bar was atomised by the PREP in an Ar atmosphere.
Plasma rotating electrode process is based on the
pulverisation of melted pool by rotation of metal bars
in contact with argon plasma arc within a controlled
Department of Metallurgical and Materials Engineering, Kocaeli
University, Umuttepe Campus, Kocaeli 41380, Turkey
Department of Mechanical Engineering, San Diego State University, San
Diego, CA 92182-1323, USA
Department of Mechatronics Education, Marmara University, Istanbul
34730, Turkey
*Corresponding author, email
ß2011 Institute of Materials, Minerals and Mining
Published by Maney on behalf of the Institute
Received 8 August 2010; accepted 17 September 2010
DOI 10.1179/1743290110Y.0000000006 Powder Metallurgy 2011 VOL 54 NO 5
atmosphere chamber of 2?5m in diameter. Argon
plasma discharge was ignited between a tungsten tip
(cathode) and the alloy bar (anode) via generated
electrical arc of 13 kV A power, fueled by flowing argon
as depicted in Fig. 1. The rotation speed of the 55 mm
anode bars were either 6000 or 12 000 rev min
producing powder with different particle size distribu-
tions. Argon plasma was used to melt the end of a
rapidly rotating bar, and then the molten droplets were
spun off and solidified during free flight in argon. Owing
to the high centrifugal force, melted metallic droplets
from the rapidly rotating bars were transformed into
spherical particles with diameters below 0?5 mm.
To minimise potential oxidation, the atmospheric
chamber was evacuated before PREP atomisation and
then purged with shielding argon gas. Atomisation
parameters are given in Table 1.
Microstructure characterisation
The evolution of the microstructure of the starting bar
and produced particles was investigated by microscopy.
All specimens were polished and etched with Kroll’s
reagent (aqueous 3% HF and 6% HNO
). Etching time
was about 5–10 s. The microstructure images were
obtained using an optical microscope (Zeiss Axiophot)
and an SEM (JEOL 6060).
Results and discussion
Determination of size distribution
Alloy powders produced at different PREP rotation
speeds resulted in an average of 1500 g per experimental
run. The powder lots were then sieved in y100 g
quantities. The SEM image of the spherical Ti–6Al–4V
alloy powder is shown in Fig. 2a. The particles have
uniform size and no satellite formation was observed.
Particle size distribution was determined by sieve
analysis. The expected inverse relationship of rotational
speed and particle size can be seen in Fig. 2b. Increased
rotational speed produced smaller sized particulate
powder. The median particle size decreased from 312
(6000 rev min
) to 168 mm (12 000 rev min
Scanning electron micrographs of powders produced by
PREP atomisation reveal homogenous spherical parti-
cles. The grain structure and morphology of the plasma
rotating electrode processed powders of different parti-
cle sizes are shown in Fig. 3. The powders were
spheroidised due to surface tension, and during the
atomisation, the droplets minimise their surface area by
1 Schematic of PREP set-up
2aSEM image of powders fabricated by PREP and
bsize distribution of powders depending on rotational
speed (cumulative volume curves)
Table 1 Atomisation parameters
Rotation speed, rev min
6000 and 12 000
Plasma gas Argon
Vacuum, mbar 10
Shielding gas Argon
Shielding gas pressure, atm 1.3
Plasma voltage, V 40
Plasma current, A 350
Bar diameter, mm 55
aparticle with no grain boundaries; bparticle with multiple grains
3 Images (SEM) of powder morphology and grain structure
Yamanoglu et al. AscastandPREPatomisedTi6Al4Valloy
Powder Metallurgy 2011 VOL 54 NO 5605
forming a sphere. The particle shape depends on
solidification time. Calculated solidification and spher-
oidisation parameters are shown in Table 2.
It is clear
that spheroidisation time is significantly shorter than the
solidification time, giving the observed spheres.
Particle size and solidification time affect the crystal
structure of an individual sphere. If the solidification rate
is sufficiently high, amorphous structure is obtained. The
SEM image of a 50 mm sized particle is shown in Fig. 3a,
giving a featureless amorphous structure. A larger
particle with a diameter of 200 mm and similar shape
required longer cooling time, and a polycrystalline
structure was obtained, as shown in Fig. 3b.
Microstructural evaluation
Optical images of typical equilibrium microstructure of
the extruded Ti–6Al–4V bar are shown in Fig. 4. The bi-
phase alloy consisting of equiaxed aand azblamellar
structures transformed from a dendritic bstructure
during solid state cooling. Bright areas are aphase
precipitated from the matrix of bphase (the dark areas).
The equiaxed aphase microstructure is more resistant
to void nucleation than the lamellar structure due to its
high ductility. Cracks nucleate within the lamellar region
more easily than in the equiaxed aphase region;
however, crack propagation is more difficult in the
lamellar structure.
High and low magnification SEM
images of a typical wrought alloy product are shown in
Fig. 5. This structure is composed of finely dispersed b
particles in a fine equiaxed grain matrix of aphase.
It is possible to control the microstructure of Ti–6Al–
4V by manipulation of cooling rates, generating various
structures from bphase region as shown in Fig. 6.
seen from the phase diagram, the structure will change
from lamellar to a9martensite if the cooling rate is
increased appropriately.
Powders produced through the PREP method pre-
sented microstructures reflecting rapid cooling. A cross-
sectional image of the atomised powder particle is shown
in Fig. 7, with a structure consisting of a9martensite.
Table 2 Solidification and spheroidisation parameters of Ti–6Al–4V powders
Rotation speed,
rev min
diameter, mm
median size, mm
median size, mm
time, ms
time, ms
6000 55 312 328 66 0.7 Sphere
12 000 55 138 164 33 0.3 Sphere
4 Optical images of as cast and extruded microstructures: bright areas are aand dark areas are bphase
5 Images (SEM) of microstructure of mill annealed hip implant
6 Structures depending on different cooling rates from b
Yamanoglu et al. AscastandPREPatomisedTi6Al4Valloy
606 Powder Metallurgy 2011 VOL 54 NO 5
A typical cross-sectional SEM image of Ti–6Al–4V
alloy powder particles is shown in Fig. 8. In preparing
the particles, nickel electrocoating is used to retain
edge definition. Clearly, these particles consist of a9
Vickers microhardness measurements were conducted to
assess the mechanical properties of plasma rotating
electrode processed powders. The electrode hardness
was measured at 2?60 GPa, while the powders of two
different particle sizes gave 2?73 (387 mm) and 3?41 GPa
(83 mm). Rapid cooling rate achieved during PREP
clearly improves obtained hardness values compared
with the original wrought bar stock.
The PREP is an advantageous method to produce fully
spherical titanium powders with minimal impurities.
Excellent flowability is accompanied with the spherical
powders, which is pertinent to metal injection moulding
and hot isostatic pressing technologies. Control of the
particle size is an indirect way to further control alloy
powder microstructure. Material hardness increases with
decreasing particle size. Manipulation of the PREP
rotation speed enables particle size control, particularly
important for utilisation of this alloy in specialised and
diverse applications.
1. Solidification characteristics of PREP atomised
powders and wrought materials have been compared.
2. Different atomisation rotation speeds have been
applied to gain various microstructural characteristics.
3. High rotational speeds in the PREP produce
smaller powders. The microstructural characteristics
can be controlled according to powder size.
4. Powders produced by PREP have higher hardness,
and the hardness increases with decreasing particle size.
1. D. R. D. Santos, V. A. R. Henriques, C. A. A. Cairo and M. D. S.
Pareira: Mater. Res., 2005, 8, 439–442.
2. V. A. R. Henriques, P. P. D. Campos, C. A. A. Cairo and J. C.
Bressiani: Mater. Res., 2005, 8, 443–446.
3. L. E. Murr, S. A. Quinones, S. M. Gaytan, M. I. Lopez, A. Rodela,
E. Y. Martinez, D. H. Hermandez, E. Martinez, F. Medina and
R. B. Wicker: J. Mech. Behav. Biomed. Mater., 2009, 2, 20–32.
4. A. Bautista, C. Moral, G. Blanco and F. Velasco: Mater. Corros.,
2005, 2, 56.
5. M. Niinomi: Mater. Sci. Eng. A: Struct. Mater.,1998,A243, 231–236.
6. N. Nomura, T. Kohama, I. H. Oh, S. Hanada, A. Chiba,
M. Kanehira and K. Sasaki: Mater. Sci. Eng. C: Biomim. Mater.
Sens. Syst., 2005, C25, 330–335.
7. M. Armendia, A. Garay, L.-M. Iriarte and P.-J. Arrazola:
J. Mater. Process. Technol., 2010, 210, 197–203.
8. S. Hata, T. Hashimoto, N. Kuwano and K. Oki: J. Phase Equilib.,
2001, 22, 386–393.
9. M. T. Jovanovic, S. Tadic, S. Zec, Z. Miskovic and I. Bobic: Mater.
Des., 2006, 27, 192–199.
10. A. Tasdemirci, A. Hızal, M. Altındis¸, I. W. Hall and M. Gu¨ den:
Mater. Sci. Eng. A: Struct. Mater., 2008, A474, 335–341.
11. E. Wosch, S. Feldhaus and T. E. Gammal: ISIJ Int., 1995, 6, 764–770.
12. P. R. Roberts: in ‘Metals handbook’, 9th edn, Vol. 7, ‘Powder
metallurgy’, 39; 1984, Materials Park, OH, ASM International.
13. R. M. German: ‘Powder metallurgy & particulate materials
processing’, 109; 2005, Princeton, NJ, MPIF.
14. X. K. Meng, Z. G. Liu, Y. Liu and G. Frommeyer: Scr. Metall.
Mater., 1995, 9, 1331–1334.
15. R. Boyer, G. Welsch and E. W. Collings (eds.): ‘Titanium alloys,
materials properties handbook’; 1994, Metals Park, OH, ASM
7aplasma rotating electrode processed Ti–6Al–4V powder and bhigher magnification of a9martensite (DIC contrast)
8 Images (SEM) of cross-sectional view of Ti–6Al–4V alloy powders (a9martensite)
Yamanoglu et al. AscastandPREPatomisedTi6Al4Valloy
Powder Metallurgy 2011 VOL 54 NO 5607
... An increase in the ejection speed reduces the mean particle size independently of the oxygen content in the atmosphere as predicted in Eq. (1) and demonstrated in studies on standard REP systems [8,13,24,25]. Results show that the variation of the incident LASER beam power densities does not affect the particle size distribution no matter the atmosphere. ...
... Each distribution, after removing irregular particles, is monomodal and is narrow ranging between 0 and 125 lm in both atmospheres. Increasing the ejection speed reduces the mean particle size independently of the oxygen content as predicted by Eq. (1) and demonstrated in studies on standard REP systems [8,13,24,25]. ...
316L grade stainless steel powders were produced by centrifugal atomization during the melting of a rotating rod heated by a high-power LASER beam. The feasibility has been demonstrated by atomizing a range of stainless steel rods. The atomization process has been observed via high-speed imaging and fragmentation regimes have been identified according to a literature review on the rotating electrode process (REP). Results were compared with literature data and an existing prediction model for such a process. High-speed observation can monitor the present process and it is shown that a solidified layer of metal is formed at the edge of the rod during the process inducing metal flake ejection due to the centrifugal stresses. Effects of incident LASER beam power density, ejection speed and oxygen content of the surrounding atmosphere on the particle size distribution and the sample surface have been studied and compared with literature data on classical REP atomizers. The study focuses on the production of irregular particles during the atomization process and highlights the influence of the oxygen content in the surrounding atmosphere on the fragmentation regime and the resulting particle size distribution.
... According to the graph (Curves (e) and (f)), only 15% of the powders produced by PREP (c) PA [20]; (d) EIGA [19]; (e) PREP [19]; (f) PREP [20]; (g) Argon atomizer [20] method consist of powders of 100 µm and below. This method is consistent with previous studies [21] in which coarser powders are produced [22,23], but are formally similar to PA in terms of their excellent sphericity, the lack of gas-filled pores. 45% of argon atomized powders (Curve (g)) are composed of 100 µm particles. ...
Full-text available
This study was carried out to investigate the possibility of titanium alloy metal powder production using low-power plasma torches. An argon DC non-transferred arc plasma torch was designed, and numerical analysis was conducted to determine the plasma jet properties and wire temperature. The highest velocities inside the nozzle attachment were between 838 and 1178 m/s. The velocities of the jets at the apex were between 494 and 645 m/s for different gas flow rates. The studied plasma gas flow rates had no significant effect on the effective plasma jet length. It was shown that the plasma jet length can be estimated by numerical analysis using the temperature and velocity changes of the plasma jet over distance. It was observed that the powders produced were spherical without any satellites. As a result of this study, a plasma torch was developed and powder production was performed successfully by using relatively low torch power.
... Vücut ortamına salınan bu metal iyonları konak canlıda iltihaplanma ya da organlarda birikerek kanserojen etkilere yol açmaktadır. Bu açıdan bakıldığında titanyum alaşımları ise yüksek özgül mukavemet değeri, korozyona karşı yüzey oksit filminin kararlı pasifliği sebebiyle mükemmel dirençleri [19][20][21] ve aynı zamanda yumuşak ve sert dokuda gösterdikleri üstün biyouyumluluk özellikleriyle metalik biyomalzemeler arasında dental ve ortopedik uygulamalarda artan bir kullanım oranına sahiptir [22][23][24]. Vücut içindeki farklı uygulama alanlarına yönelik olarak titanyum esaslı biyomalzemeler sahip olduğu çok farklı kompozisyon alternatifleri ile ön plana çıkmaktadır. Bu noktada ortopedik uygulamalar için sıklıkla tercih edilen titanyum alaşımlarından olan ve α+β faz yapısına sahip Ti-6Al-4V alaşımından (ASTM F1108) özgül mukavemet, korozyon direnci ve biyouyumluluk özellikleri açısından üstün performansa sahip bir yapısal biyomalzeme olarak söz edilebilir [25]. ...
Full-text available
The biomedical material industry continues to grow worldwide for people to sustain their quality of life and related activities. The increase in the aging population and prosperity level are among the main reasons that the biomedical material industry growing rapidly. According to the characteristic properties of the region where implantation will be performed within the body, the preferred material group varies. Among these materials, metallic biomaterials have a high usage rate due to their superior mechanical properties. As with the issues faced in polymer-based, ceramic-based, and composite materials the problems triggered by metallic biomaterials in patients take place by cause of many reasons. Innovative solutions are produced today with the developing technology and the effort done against to the problems. Whereas metallic biomaterials cause biomechanical unsuitability with their high modulus of elasticity, they threaten biocompatibility by producing a poisonous effect because of toxic alloy element ions. Therefore, the characteristics of β-type Ti alloys were explored which were created to address two basic issues: they were alloyed with elements with excellent biocompatibility and had a low modulus of elasticity owing to their phase structure. Furthermore, the effects of the production methods on β-type Ti alloys were highlighted and the effectiveness of alloys created with powder metallurgy technology was analyzed at this step. Keywords: Biomaterials, titanium based materials, modulus of elasticity, powder metallurgy.
... Ceramics and polymeric materials are not suitable for load-bearing applications due to their brittleness and low mechanical properties, respectively [1]. On this point, among the metallic materials, it is easy to imagine that titanium alloys are the most attractive materials for osseointegration applications due to their excellent properties [2][3][4]. ...
Metallic biomaterials improve the life quality of the people. In particular, efforts to develop porous biomaterials are getting more attention recently. Among the metallic materials, titanium alloys are commonly preferred in biomedical application due to their excellent biocompatibility, high corrosion resistance and mechanical strength. Researches into porous titanium-based implant materials have resulted in several fabrication methods, with many others under development. In this study, powder metallurgical different processing techniques such as partial sintering of powders, replication, additive manufacturing, plasma spray coating, microwave sintering, space holder method, spark plasma sintering, metal injection molding were investigated. What are the requirements, problems and developments in this field? After considering these issues, we will discuss different conventional and technological processing methods, along with their effects on the structure and properties of implant materials.
... This is because the size distributions of powders by PREP are narrow and easy to modify [5,6]. Previous reports have indicated that the particle size distribution of PREP powders is primarily dependent on the parameters of rotating speed and heat parameters [7,8]. ...
Full-text available
In the present study, Ti6Al4V spherical powders were prepared by supreme-speed plasma rotating electrode process and the particle size fit log-normal distribution. The average diameter of the powders was successfully determined by a model developed in this work, suggesting that the particle size distribution is mainly affected by the rotating speed. The log-normal distribution factor of the particle size distribution maintains stable as the rotating speed ω varies. The particle size distribution indicates that the main atomization mode of Ti6Al4V under supreme-speed plasma rotating electrode process is of the characteristics of direct drop formation. The mechanical properties of the samples prepared by selective laser melting of Ti6Al4V powders were characterized, indicating that such Ti6Al4V samples with isotropy structure exhibit high yield strength and good ductility. Keywords: Particle size distribution, Atomization, Ti6Al4V, Plasma rotating electrode process, Selective laser melting, Rapid solidification
... Ti alloys are generally produced by casting, forging, and powder metallurgical techniques. Powder metallurgical production techniques of producing Ti alloys provide advantages such as faster and near net shape production cycle [4]. ...
Full-text available
In this research, the effect of Ag on the mechanical properties of Ti5Al2.5Fe alloy has been investigated. The Ti5Al2.5Fe alloy, with different amounts of Ag ranged from 1 to 5 wt. % was prepared by mechanical mixing and then fabricated by hot pressing at 950 oC for 15 min under 50 MPa. Three holding steps were applied to the powder compacts to restrain the liquid phases inside graphite die before reaching the maximum sintering temperature. The sintered samples were subjected to hardness, bending and wear tests to study the effect Ag on the mechanical properties of Ti5Al2.5Fe alloy. The microstructural characterization was carried out by means of the optical and scanning electron microscope. The results showed that Ag played a differential role in the mechanical properties supported by microstructural constituents. The bending strength and hardness of the produced samples increased with the addition of Ag, the hardness of the alloys then tends to decreased with increasing Ag content but still remained above the hardness of Ti5Al2.5Fe alloy. Wear test also showed similar trends with hardness test results. Finally, the optimum Ag content for the Ti5Al2.5Fe alloy has been determined as 1 wt.%. XRD analysis showed that unsolved Ag content was the main reason for the decrease in mechanical properties.
Ti-based alloy powder is an excellent candidate as an additive manufacturing material, owing to its high strength-to-weight ratio, corrosion resistance and biocompatibility. However, molten Ti is highly reactive with ceramic crucibles. Thus, only crucible-free techniques can be used, limiting the manufacturing. In this study, Ti–Y, CP-Titanium powder was manufactured using the vacuum induction gas atomization cold crucible (VIGA-CC) process, without using any master alloy; moreover, its properties were elucidated. Characterisations were performed to comparatively analyse the surface morphology, impurity content and mechanical properties of the synthesised powder. It was found that the powder had a uniform composition and was refined by the yttrium addition. The VIGA-CC process, by which alloy powders with various compositions can be prepared, is expected to expand the list of target alloys that can be used in additive manufacturing processes.
In the current study, the effect of Mo content (1-10 wt.%) on the microstructure, hardness, bending and wear properties of Ti6Al4V-xMo alloys was investigated. The pre-alloyed and Plasma Rotating Electrode Process (PREP) atomized Ti6Al4V alloy powders and elemental Mo particles were mechanically mixed for 45 min in a zirconia jar. A uniaxial vacuum hot pressing was applied at 950°C for 30 min under 50 MPa pressure. The Ti6Al4V-xMo alloys were prepared metallographically and characterized by optical and scanning electron microscopy. The chemical composition of the different zones in the structure was determined using energy-dispersive x-ray (EDX) analysis. Mo appeared among the TiAl64V alloy particles and caused the formation of different diffusion zones. The formation of grain boundary α was effectively prevented, and instead, fine α’ and β zones were formed. Various phases formed along the particle boundaries of the Ti6Al4V alloy, and effective improvements in hardness, bending and wear resistance were obtained. However, the highest Mo content caused a decrease in mechanical properties. Ti6Al4V-5Mo alloy showed superior hardness and wear resistance.
Conference Paper
With the rapid advancement of technologies in recent years, the use of additive manufacturing methods is increasing rapidly. Additive manufacturing technologies, which have been used for product development and prototyping for years, have replaced by conventional manufacturing technologies especially small and personalized applications. The quality of parts produced by metal additive manufacturing technologies directly is affected the size, shape, and purity of the metal powder used in production. These properties of metal powders are controlled by powder production techniques. Accordingly, in this study, production methods of metal powders used as a raw material in metal additive manufacturing technologies were investigated. The properties of metal powders have been determined to produce defect-free parts in metal additive manufacturing methods. Information is given about the production technologies that can provide these features.
Conference Paper
Full-text available
Son yıllarda teknolojinin hızla ilerlemesiyle, eklemeli imalat yöntemlerinin kullanımları hızla artmaktadır. Yıllarca ürün geliştirme ve prototip amaçlı kullanılan eklemeli imalat teknolojileri, günümüzde özellikle az adetli ve kişiye özel uygulamalarda konvansiyonel imalat teknolojilerinin yerini almıştır. Eklemeli metal imalat teknolojilerinde üretilen parça kalitesini, üretimde kullanılan metal tozunun özellikle boyut, şekil ve saflık özellikleri doğrudan etkilemektedir. Metal tozlarının bu özellikleri toz üretim teknikleri üzerinden kontrol edilir. Bu doğrultuda, bu çalışmada, eklemeli metal imalat teknolojilerinde hammadde olarak kullanılan, metal tozlarının üretim yöntemleri araştırılmıştır. Eklemeli metal imalat yöntemlerinde hatasız parça imalatı yapılabilmesi için metal tozlarının sahip olması gereken özellikler belirlenmiştir. Bu özellikleri sağlayabilen üretim teknolojileri ile ilgili bilgi verilmiştir.
Full-text available
Titanium alloys have several advantages over ferrous and non-ferrous metallic materials, such as high strengthto-weight ratio and excellent corrosion resistance. A blended elemental titanium powder metallurgy process has been developed to offer low cost commercial products. The process employs hydride-dehydride (HDH) powders as raw material. In this work, results of the Ti-35Nb alloy sintering are presented. This alloy due to its lower modulus of elasticity and high biocompatibility is a promising candidate for aerospace and medical use. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by isochronal sintering between 900 up to 1600 °C, in vacuum. Sintering behavior was studied by means of microscopy and density. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Samples sintered at high temperatures display a fine plate-like a structure and intergranular b. A few remaining pores are still found and density above 90% for specimens sintered in temperatures over 1500°C is reached.
Full-text available
Titanium alloys parts are ideally suited for advanced aerospace systems because of their unique combination of high specific strength at both room temperature and moderately elevated temperature, in addition to excellent corrosion resistance. Despite these features, use of titanium alloys in engines and airframes is limited by cost. The alloys processing by powder metallurgy eases the obtainment of parts with complex geometry. In this work, results of the Ti-6Al-4V and Ti-13Nb-13Zr alloys production are presented. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 up to 1500 °C, in vacuum. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. It was shown that the samples were sintered to high densities and presented homogeneous microstructure from the elements dissolution with low interstitial pick-up.
It can be concluded from the present investigation that the high stress near the crack tip can be relaxed by a slip of dislocations in TiAl or Ti3Al lamellae when crack grows along the lamellar TiAl/Ti3Al phase boundary, hence, crack that propagated in the lamellar TiAl/Ti3Al structure is ductile rather than brittle. The ductile crack propagation in the lamellar structure plays a significant role in improving the ductility of the two-phase TiAl based alloys.
Porous Ti alloy compacts were fabricated and their microstructure and mechanical properties were investigated in this study. Ti alloy powders were atomized from Ti–15Mo–5Zr–3Al (wt.%) bar using the plasma rotating electrode process (PREP) in an Ar atmosphere. These alloy powders were sintered under 1–30 MPa at 1223 K for 7.2 ks by hot-pressing (HP). These compacts were solution treated at 1223 K for 1.2 ks, and then quenched into iced water (STQ). X-ray diffraction analysis revealed that a small amount of α phase appeared in the β phase of the HP compacts, while not in the STQ compacts. Young's modulus of STQ compacts is lower than that of HP compacts. It was found that the strength of porous Ti–15Mo–5Zr–3Al is higher than those of porous pure Ti and human cortical bone, as compared in the range from 10 to 30 GPa of Young's modulus for human bone.
Microstructures of Ti50Al45Mo5 (at.%) alloy powders produced by the plasma rotating electrode process (PREP) were investigated. The powders have inhomogeneous structures, which consist of dendrites and rounded grains. The dendrites, which show a “rosettelike” morphology, are formed on the powder surface and around the rounded grains. The rosettelike dendrites are of hexagonal α 2 (D019) phase even though the dendrites have an equiaxial morphology, and a small amount of β 2 (B2) phase is also contained inside. It is suggested that the solidification to α (hcp-A3) phase occurred by the peritectic reaction between the primary β (bcc-A2) dendrites and the liquid: L+β→L+β+α. The rounded grains, on the other hand, are of β 2 phase in which acicular α or α 2 laths are precipitated with the Burgers orientation relationship. Antiphase domain boundaries in the β 2 matrix are intersected by α(α 2) laths. It is interpreted that the α(α 2) laths were formed by the solid-state transformations: β 2→β 2+α→β 2+α 2. The formation of the two different microstructures in the powder particles is rationalized in terms of the changes in local composition of the liquid phase during the rapid solidification process.
The Plasma-Rotating-Electrode-Process (PREP) is based on the pulverization by rotation of metal bars in contact with a Ar/N-2 plasma are. Due to the high centrifugal forces of the rapidly rotating bars, high nitrogen steel powders are produced with diameters in the range of 0.02 to 0.5 mm. The low diameters and the high centrifugal forces, as well as the high particle velocities, cause the steel droplets to cool down rapidly in the reactor chamber. Mathematical calculations show that cooling rates of up to 10(5) K/s are attained. It is demonstrated that the cooling rate of all powder particles and the structures produced can be predicted.
The high strain rate (220-550 s(-1)) and quasi-static (0.0016 s(-1)) compression deformation behavior of a sintered Ti6Al4V powder compact was investigated. The compact was prepared using atomized spherical particles (100-200 mu m) and contained 38 +/- 1% porosity. The deformation sequences of the tested samples were further recorded by high speed camera and analyzed as a function of strain. The failure of the compact, which was found to be similar in the studied high strain rate and quasi-static strain rate testing regimes, occurs through particle decohesion along the surface of the two cones in a ductile (dimpled) mode consisting of void initiation and growth and by void coalescence in the interparticle bond region. The effect of strain rate was to increase the flow stress and compressive strength of the compact while the critical strain corresponding to the maximum stress was shown to be strain rate independent. (C) 2007 Elsevier B.V. All rights reserved.
Production of investment castings of titanium alloys was considerably increased during last years due to the significant cost savings compared to complicated machined parts. However, the disadvantage of as-cast titanium alloys is that the heat-treatment remains only a limited option for improvement of their properties. The object of this paper was to study the effect of heat-treatment of investment cast Ti–6Al–4V alloy performing X-ray diffraction analysis, light microscopy and quantitative metallography together with hardness and room temperature tensile tests. The effect of annealing temperatures (above and below β transus temperature) and cooling rates on microstructure and mechanical properties was discussed in terms of the β → α transformation. The results of this paper also show that, besides heat treatment parameters, melting and casting practice together with mold technology strongly influence the properties of castings.