Effect of Textures on Tensile Properties of Extruded Ti64/VGCF Composite by Powder Metallurgy Route

International audienceMonolithic Ti-6Al-4V and Ti-6Al-4V composited with vapor grown carbon fibers (VGCFs) were fabricated by powder metallurgy (P/M) route in this research. Spark plasma sintering (SPS) subsequent by hot extrusion was applied in order to fabricate a full-density and high strength composite materials. A severe plastic deformation during hot extrusion resulted in a dynamic recrystallization (DRX) in α-Ti grains. Dynamic recrystallization was observed in a low deformation temperature region, which yield point of material was also observed in the stress-strain curve. Furthermore, the addition of VGCFs encouraged the dynamic recrystallization during hot extrusion. Ti64+0.4 wt-% VGCFs shows the highest tensile strength of 1192 MPa at the end part of the extruded rod where the temperature of material was lower compared to the tip and middle part during extrusion. Additionally, the improvement in tensile strength was contributed by solid-solution strengthening of carbon element originated from VGCFs in α-Ti matrix. Introduction. Ti-6Al-4V alloy (Ti64) is the most well-known among Ti alloys, and used in many industries. High specific strength, good corrosion resistance and biocompatibility promoted a widely use of Ti and its alloys such as in aerospace and automobile industries, or medical devices and prosthesis [1, 2]. Many researchers studied the effect of hot working on microstructure and mechanical properties of wrought or cast Ti64. A. Momeni et al. studied the effect of deformation temperature and strain rate on microstructure and flow stress of wrought Ti64 under hot compression test [3]. Ti64 specimens, which experienced a hot compression test at 1273 and 1323 K, exhibited a large recrystallized α-grain with low flow stress on the microstructure. This correlated with the results proposed by T. Seshacharyulu et al. and R. Ding et al. for the cast Ti64 [4, 5]. G.Z. Quan et al. studied the modelling for dynamic recrystallization in Ti-6Al-4Al by hot compression test. The result shows that a flow stress decreases with the increasing of deformation temperature. The high deformation temperature promotes the mobility at the boundaries for annihilation of dislocation, and the nucleation and growth of dynamic recrystallization [6]. H.Z. Niu et al. studied the phase transformation and dynamic recrystallization (DRX) behaviour of Ti-45Al-4Nb-2Mo-B (at-%) alloy. The results show that the DRX modes were strongly depends on deformation temperature, and a decomposition of lamellar structure along with the DRX of γ and B2/β grain occurred at low forging temperature [7]. D.L. Ouyang et al. studied the recrystallization behaviour of Ti-10V-2Fe-3Al alloy after hot compression test. They reported that a partial grain refinement related to incomplete DRX was observed even after a large strain of 1.6, and an increment of strain resulted in an increasing of volume fraction of recrystallized grain. The full grain refinement accompanied by the completely DRX was developed at lower temperature of 1223 K by severe deformation [8]. The dynamic recrystallization behaviour of Ti-5Al-5Mo-5V-1Cr-1Fe alloy was reported by H. Liang et al. The DRX always occur when the store energy in a material reaching the critical value. During hot deformation, the increase of flow stress caused by dislocation generation and interaction resulted in an improvement of strength of Ti alloys. The sample deformed at 1073 K exhibited higher tensile strength compared to sample deformed at 1153 K because more dislocations were generated [9]. There are many reports related to dynami

Corrosion Behavior and Strength of Dissimilar Bonding Material between Ti and Mg Alloys Fabricated by Spark Plasma Sintering

Ti and solution treated Mg alloys such as AZ31B (ST), AZ61 (ST), AZ80 (ST) and AZ91 (ST) were successfully bonded at 475 °C by spark plasma sintering, which is a promising new method in welding field. The formation of Ti3Al intermetallic compound was found to be an important factor in controlling the bonding strength and galvanic corrosion resistance of dissimilar materials. The maximum bonding strength and bonding efficiency at 193 MPa and 96% were obtained from Ti/AZ91 (ST), in which a thick and uniform nano-level Ti3Al layer was observed. This sample also shows the highest galvanic corrosion resistance with a measured galvanic width and depth of 281 and 19 µm, respectively. The corrosion resistance of the matrix on Mg alloy side was controlled by its Al content. AZ91 (ST) exhibited the highest corrosion resistance considered from its corrode surface after corrosion test in Kroll’s etchant. The effect of Al content in Mg alloy on bonding strength and corrosion behavior of Ti/Mg alloy (ST) dissimilar materials is discussed in this work