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

Structural Characteristics and Crystallization of Metallic Glass Sputtered Films by Using Zr System Target

Zr-Al-Ni-Cu thin films were deposited by the radio-frequency sputtering method at low substrate temperature using three kinds of targets: Zr55Al10Ni5Cu30 bulk metallic glass target (α-BMG target), crystallized bulk metallic glass target (c-BMG target), and an elemental composite target composed of each Zr, Al, Ni chips, and Cu plate. XRD profiles of the films prepared when using these targets indicated that all of the films showed amorphous structures. While XRD profiles of the films using α- and c-BMG targets revealed a broad peak of 2θ=38 degree in the same way as the α-BMG target indicating amorphous structures, that of the film using elemental composite targets showed a broad peak of 2θ=42 degree, which is higher compared to the latter material. As a result of annealing the films at various temperatures for 900 seconds, the film using the α-BMG target showed a crystallization temperature of 748 K, higher than that of BMG with 723 K, while the other films had lower crystallization temperatures below 723 K. XRD profiles also indicated that the crystallized compounds of the films were different from those of BMG target

CNTs/TiC Reinforced Titanium Matrix Nanocomposites via Powder Metallurgy and Its Microstructural and Mechanical Properties

By using pure titanium powder coated with unbundled multiwall carbon nanotubes (MWCNTs) via wet process, powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with the CNTs was prepared by spark plasma sintering (SPS) and subsequently hot extrusion process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyzer. The mechanical properties of TMC were significantly improved by the additive of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of tensile specimens were analyzed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed

High-temperature properties of extruded titanium composites fabricated from carbon nanotubes coated titanium powder by spark plasma sintering and hot extrusion

Pure titanium matrix composite reinforced with carbon nanotubes (CNTs) was prepared by spark plasma sintering and hot extrusion via powder metallurgy process. Titanium (Ti) powders were coated with CNTs via a wet process using a zwitterionic surfactant solution containing 1.0, 2.0 and 3.0 wt.% of CNTs. In situ TiC formation via reaction of CNTs with titanium occurred during sintering, and TiC particles were uniformly dispersed in the matrix. As-extruded Ti/TiCs composite rods were annealed at 473 K for 3.6 ks to reduce the residual stress during processing. After annealing process, the tensile properties of the composites were evaluated at room temperature, 473, 573 and 673 K, respectively. Hardness test was also performed at room temperature up to 573 K with a step of 50 K. The mechanical properties of extruded Ti/CNTs composites at elevated temperature were remarkably improved by adding a small amount of CNTs, compared to extruded Ti matrix. These were due to the TiC dispersoids originated from CNTs effectively stabilized the microstructure of extruded Ti composites by their pinning effect. Moreover, the coarsening and growth of Ti grain never occurred even though they were annealed at 573, 673 K for 36 ks and 673 K for 360 ks, respectively