[Show abstract][Hide abstract] ABSTRACT: This work investigates the effect of microstructure on tensile properties and corrosion behavior of a Zr–Sn–Nb–Fe–Cu–O alloy. Scanning electron microscope, transmission electron microscope, electron back scattering diffraction, tensile tests and autoclave corrosion test were jointly carried out to characterize in detail the microstructural features and properties of the alloy studied. The corrosion rate constant increases with decreasing the degree of recrystallization. The sample with slower evolution of undulated interface exhibits higher tensile strength and possesses better corrosion resistance. The plasticity of sample can hardly be the rigorous limitation on corrosion performance, which is attributed to the consistent consummation of the deformed substrate around the interface during corrosion to make the inner undeformed substrate become fresh interface. Furthermore, second phase particles (SPPs) may play a role in the nucleation of cracks in the oxide.
Full-text · Article · Jan 2016 · Materials & design
[Show abstract][Hide abstract] ABSTRACT: Sandwich architecture with cross-shape periodic cellular cores is synthesized via eutectic reaction between NiTi and Nb powder, such forming metallurgical bonding between NiTi wires near eutectic reaction temperature. Superelasticity is investigated systematically via nanoindentation tests. The Ti-rich phase is weaker in superelastic recovery comparing with that of Nb-rich phase, lamellar and rod-like NiTi-Nb eutectic. Inconsistent Nb element distribution in the interface of eutectic area and NiTi wire enhances the martensitic transformation.
[Show abstract][Hide abstract] ABSTRACT: Direct laser fabrication (DLF) is one of the advanced near-net shape processing technologies. The variations of laser parameters can change the energy distribution within a laser scan, and thus affect the cooling rate, and resulting microstructure of deposited material. In this study, the effect of the laser parameters on the microstructure of additive laser fabricated Ti6Al4V alloy was investigated. It was found that huge columnar grains formed during laser fabrication of Ti6Al4V alloy for a wide range of processing conditions, and the laser power, scanning speed and duration time were had a significant effect on the refinement of the prior grains. Gradient morphologies were obtained from a complex thermal history.
[Show abstract][Hide abstract] ABSTRACT: The incorporation of ceramic particulate reinforcements into titanium alloys can improve the specific strength and specific stiffness, while inevitably reduce the plasticity and ductility. In this study, in situ synthesized multilayer Ti-(TiB+La2O3)/Ti composite was designed by learning from the microstructure of nature biological materials with excellent mechanical properties. The Ti-(TiB+La2O3)/Ti composite with unique characteristic of laminated structure was prepared by combined powder metallurgy and hot rolling. The method has the synthesize advantages with in-situ reaction of Ti and LaB6 at high temperature and controllability of reinforcements size and constituent phases in composites. The result shows that the pores in the as sintered laminated structure composite completely disappeared after hot rolling at 1050°C. The agglomerated reinforcement particles were well dispersed and distributed uniformly along the rolling direction. The thickness of pure Ti layer and (TiB+La2O3)/Ti composite layer decreased from 1mm to about 200μm. Meanwhile, the grains size was refined obviously after rolling deformation. The room temperature tensile test indicates that the elongation of the laminated Ti-(TiB+La2O3)/Ti composite improved from 13% to 17% in comparison with the uniform (TiB+La2O3)/Ti composite, while the tensile strength had little change. It provides theoretical and experimental basis for fabricating the novel high performance laminated Ti-(TiB+La2O3)/Ti composites.
Full-text · Article · Nov 2015 · Progress in Natural Science
[Show abstract][Hide abstract] ABSTRACT: This paper investigates the effect of alloyed Si on the autoclave corrosion performance and corrosion mechanisms of Zr-Sn-Nb-Fe-O alloys. Quantitative analyses are performed on the microstructure of alloys and their oxide behavior. The Si-containing alloy possesses improved corrosion resistance. The reason is that a trace of Si enhances the strength of alloy and thus slows the evolution of undulated interface of oxide/metal which is associated with the formation of cracks in the oxide. The generation of cracks is discussed in further detail in relation to corrosion kinetics. This work advances the understanding of improving the corrosion resistance of zirconium alloys.
Full-text · Article · Nov 2015 · Corrosion Science
[Show abstract][Hide abstract] ABSTRACT: A Zr-Sn-Nb-Fe-Si-O alloy was prepared and its microstructure, corrosion properties, hydrogen pick-up, and mechanical behavior were investigated and correlated. Both the conventional rolled and annealed specimens (Group A) and the second β-quenched specimens (Group B) possess proper corrosion resistance and hydrogen pick-up capability within 200 days exposure in LiOH aqueous solution, which are related to the suitable chemical composition, partial recrystallized microstructure and fine second phase particles. Group A at 380. °C has slightly larger ductility in elongation than that at room temperature, whilst the elongation of Group B at 380. °C increases nearly twice of that at room temperature.
Full-text · Article · Oct 2015 · Corrosion Science
[Show abstract][Hide abstract] ABSTRACT: Fatigue crack growth tests of NiAl bronze (NAB) alloy heat treated at different temper temperature after quenching at 920 °C are performed using direct current potential drop method. The influences of heat treatment on the fatigue crack growth behavior of NAB alloy are investigated. The results show that the fatigue crack growth rate (FCGR) of NAB alloy decreases with the increase of temper temperature. A few large secondary cracks are obtained as the sample is tempered at 350 °C and the secondary cracks diminish with the increase of temper temperature. With further increasing temper temperature to 550 °C, a large number of small secondary cracks are obtained, which is responsible for its lower FCGR. The as-cast NAB alloy has a lower FCGR than that tempered at 550 °C at low stress intensity factor range (ΔK) region, and the lower FCGR is attributed to the crack deflection effect of the as-cast microstructure. At high ΔK region, the crack deflection effect diminishes, which leads to the higher FCGR of as-cast sample.
Full-text · Article · Sep 2015 · Journal of Materials Research
[Show abstract][Hide abstract] ABSTRACT: NiAl bronze (NAB) alloy is prepared by using friction stir processing (FSP) technique at a tool rotation rate of 1200 rpm and a traverse speed of 150 mm/min. A post heat treatment is performed at the temperature of 675 °C. The effect of heat treatment on the microstructure and microhardness is studied. The results show that the microstructure of the FSP NAB alloy consists of high density dislocations, retained β phase (β’ phase) and recrystallized grains. When annealed at 675 °C, discontinuous static recrystallization (DSRX) takes place. The content of β’ phase gradually decreases and fine к phase is precipitated. After annealing for 2 h, both the microhardness of the FSP sample in the stir zone (SZ) and the difference in hardness between the SZ and base metal decrease due to the reduction of the dislocation density and β’ phase, accompanying recrystallized grain coarsening. With further increasing of the annealing time to 4 h, the aforementioned difference in hardness nearly disappears.
No preview · Article · Sep 2015 · Metals - Open Access Metallurgy Journal
[Show abstract][Hide abstract] ABSTRACT: Titanium matrix composites were prepared by investment casting in a consumable arc skull casting furnace. With the addition of B4C, the average primary β grains are refined, and the morphology of α phase tends to be more equiaxed. The free energy for nucleation consisting of the bulk free energy, orientation-independent interfacial energy, and elastic strain energy is calculated to investigate the role of nucleation sites in determining the shape of critical nucleus. In the current study, the TiB whiskers were found to be arranged in the grain boundary and provide heterogeneous nucleation sites for α precipitates, and the interfacial energy is about 14 % more than that in Ti-64, while its elastic strain energy is reduced to about three quarters of the latter one.
No preview · Article · Sep 2015 · Journal of Materials Science
[Show abstract][Hide abstract] ABSTRACT: The influence of phases with different morphology and mechanical properties on fatigue crack growth behavior in nickel aluminum bronze (NAB) has been investigated. Annealing at 675°C and normalizing at 920°C heat treatments were used to produce different morphologies and fractions of second phases. This analysis shows that the coarse dendritic κII particles and κIII lamellae as hard brittle phases in as-cast and annealed NAB have an accelerative effect on the fatigue crack propagation where by cracks propagate through α and κII/κIII interface. Fatigue cracks in normalized NAB prefer to propagate through the ductile α grains, form fatigue striations and have the lowest crack growth rate. The uniformly distributed, fine κIV precipitates in the α grains improves fatigue crack growth resistance. This work identifies the role of NAB second phases on propagation of fatigue cracks, and provides suitable heat treatment for improving fatigue crack resistance in terms of controlling second phase type, distribution and percentage.
No preview · Article · Sep 2015 · International Journal of Fatigue
[Show abstract][Hide abstract] ABSTRACT: In this study, the forged NiAl bronze (NAB) were hot rolled with the deformation degree of 40%, 60%, 80%, 90% and 95% at 850. °C, respectively. Effects of rolling deformation degree on the microstructure and mechanical properties of the NAB alloy were investigated. Scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) methods were used to characterize the microstructure. The results show that α grains are refined by the dynamic recovery and recrystallization, penetration of β phase into α phase and particle-stimulated nucleation (PSN) of recrystallization during rolling. The refined grains make a main contribution to the increase of mechanical properties of rolled NAB. When the deformation degree is increased to 80%, the optimum tensile properties with ultimate strength of 861.3±8.5. MPa, yield strength of 634.5±7. MPa and elongation of 19.3±0.05% is obtained. With further increasing the deformation degree, the strength of rolled NAB alloy increase and the elongation decrease due to the increase of work hardening effect and the formation of martensitic nano-twins.
No preview · Article · Sep 2015 · Materials Science and Engineering A
[Show abstract][Hide abstract] ABSTRACT: NiAl bronze (NAB) was produced using the friction stir processing (FSP) technique at various tool rotation rates (ω) and traverse speeds (v). Optical microstructure (OM) observation results indicated that inhomogeneous microstructures were produced from top to bottom in the stir zone (SZ), cavity defects were found in the retreating side (RS) area due to inadequate fill of NAB material flow during FSP. Results indicate that FSP processing parameters have a significant influence on the microstructure of NAB alloy. An optimized FSP processing map was obtained from the analysis of the pseudo heat index ω2/v. Five optimum processing parameters were selected from the processing map, which were used to investigate the effect of FSP parameters on the corrosion properties of NAB by the salt fogging corrosion test. It was determined that the corrosion properties were improved by decreasing the rotation rate at a constant traverse speed, and the grain size and the volume fraction of retained β phases were reduced by using the optimum FSP parameters. These results could optimize the microstructure and deepen the understanding of the corrosion behavior of FSP NAB.
No preview · Article · Sep 2015 · MATERIALS TRANSACTIONS
[Show abstract][Hide abstract] ABSTRACT: Equal channel angular pressing provides a convenient approach to introduce ultrafine grain size into commonly used metallic materials. In this study, equal channel angular pressing of (TiB+TiC)/TC18 composite was carried out under different passes via route Bc. Microstructure evolution is systematically investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that grain boundary sliding contributes much to the plastic deformation and grains are refined largely to 100nm for (TiB+TiC)/TC18 with 0.2% B4C addition after two passes. The appearance of dislocation accelerates the transformation of spherical α recrystallized grains. Sufficient recrystallization is obtained after three passes. Tensile tests show that both high strength and elongation appear in the specimen with 0.2wt% B4C addition, which is deformed repeatedly after three passes. Equal channel angular pressing thus be a viable mode for producing titanium matrix composite with both high strength and ductibility.
Full-text · Article · Aug 2015 · Materials Science and Engineering A
[Show abstract][Hide abstract] ABSTRACT: (TiB + TiC)/TC4 composites reinforced with different amounts of TiB whiskers and TiC particles are produced by common casting and hot forging technology. Then the fracture toughness of (TiB + TiC)/TC4 composites is analyzed by experiment and modeling. The experimental results indicate that not only reinforcement volume fraction but also the mole ratio between TiB whiskers and TiC particles can influence the fracture toughness of (TiB + TiC)/TC4 composites. Microstructure observations are carried out to examine the behavior of TiB whiskers and TiC particles in the fracture process. An analytical expression for predicting the fracture toughness of (TiB + TiC)/TC4 composites is built up. In particular, the coupling influences of TiB whiskers and TiC particles on the elastic modulus, yield strength, and fracture strain of TMCs are revealed in the modeling process. The results indicate that when TiB and TiC particles are coexisting in the TMCs, the fracture toughness of (TiB + TiC)/TC4 composites increases with the increase of the TiB whiskers aspect ratio, TiC particles volume fraction and size; however, with the increase of TiB whiskers volume fraction, the fracture toughness decreases. The breakage of TiB whiskers is the main reason for the fracture of TMCs. The acting mechanism of TiC particles on the fracture of TMCs transfers from blocking crack propagation and interfacial debonding to breakage with the increase of size, which can decrease the fracture toughness of (TiB + TiC)/TC4 composites. Considering the broken fraction of TiB whiskers, the fracture toughness of (TiB + TiC)/TC4 composites can be reasonably predicted.
Full-text · Article · Aug 2015 · Metallurgical and Materials Transactions A
[Show abstract][Hide abstract] ABSTRACT: The effect of low-temperature pre-deformation on the microstructural evolution of a Zr–Sn–Nb–Fe–Cu–O alloy was investigated by optical metallography, scanning electron microscope, transmission electron microscope, and electron backscattering diffraction (EBSD). It is found that a reasonably homogeneous and fine equiaxed grain structure with uniformly distributed second-phase particles (SPPs) can be obtained in 40% pre-deformed samples (Group A) but not in directly hot-rolled ones (Group B) after hot rolling. The initial SPPs diameter in Group A is also reduced. Noticeable differences in microstructural evolutions including the distribution and size of SPPs, grain size of matrix, and texture are observed between both groups. Reasons for such discrepancies are attributed to the defects (such as dislocations and interfaces) introduced during the pre-deformation and more preferred precipitation sites formed in Group A. The aging after the pre-deformation results in new slip systems activated during hot rolling, leading to more thorough refinement of grains. In addition, the growth of SPPs is interpreted by the Lifshitz–Slyozov–Wagner model.
Full-text · Article · Jul 2015 · Journal of Nuclear Science and Technology
[Show abstract][Hide abstract] ABSTRACT: In this study, equal channel angular pressing (ECAP) of (TiB + TiC)/Ti6Al4V titanium matrix composite was successfully carried out at 800 °C, the effect of pass number on the microstructure and mechanical properties was investigated. After each pass of ECAP, the evolution of the microstructure and mechanical properties of (TiB + TiC)/Ti6Al4V composite during thermal-mechanical processing was studied, the Vickers micro-hardness measurements and tensile testing were performed at room temperature. The results showed that the size of the reinforcements and grains were both fully refined to a smaller scale, a number of more homogeneous TiB short fibers and TiC particles have been attained after four ECAP passes. The tensile strength increased with increasing ECAP numbers and saturated after four ECAP passes to a yield strength of 1200 MPa, and microhardness was also significantly improved by means of this processing technology, the ductility of titanium matrix composite after the four ECAP passes was slightly greater than the first ECAP pass.
Full-text · Article · Jun 2015 · Materials and Design
[Show abstract][Hide abstract] ABSTRACT: First-principle calculations were carried out on the ternary of sodium aluminium silicide to evaluate the elastic properties and electronic structures within the framework of the density functional theory. Six independent elastic constants were obtained from the coefficients of the polynomials determined by non-linear least squares fitting of the energy-strain functions, and the elastic parameters of the corresponding polycrystalline aggregates were estimated from the calculated single crystal elastic constants. The electronic structure and charge density distribution were explored to analyse and explain the nature of chemical bonding. The results showed that the sodium aluminium silicide compound is a mechanically stable and brittle material with a metallic character. The nature of the bonds formed a layer structure, with a layer of covalent bonding between the Si and Al atoms alternating with a Na atom layer which bonded the Al–Si layer by ionic interaction.
No preview · Article · May 2015 · Material Research Innovations
[Show abstract][Hide abstract] ABSTRACT: In this paper, the morphologic evolution of α-phases and their influence on mechanical properties during the hot working process of the Ti-6Al-4V alloy has been quantitatively investigated. Samples with a variety of different features of α-phase were obtained by hot working. A quantitative analysis of SEM/OM images is carried out to determine the features of α-phase before and after deformation, including the length, thickness, aspect ratio and volume fraction of α-phase. It was found that the α-phase platelet thickness increases with the increasing of forging height reduction on subsequent solution and aging treatment, larger height reduction would reduce the aspect ratio and length of α-phase and further makes the α-phase closest to equiaxed morphology. Moreover, the influence of the α-phase features on the mechanical properties was systematically investigated. The results indicate that the mechanical properties are strongly determined by the features of the α-phase, especially the thickness and volume fraction of the α-phase. This work will optimize the mechanical property by means of microstructural control and deepen the understanding of influence of α-phase features on the mechanical properties.
Full-text · Article · Apr 2015 · International Journal of Modern Physics B