Cold Consolidation of Ball-Milled Titanium Powders Using High-Pressure Torsion

Abstract

KAVEH EDALATI, ZENJI HORITA, HIROSHI FUJIWARA, and KEI AMEYAMA Pure Ti (99.5 pct) powders after processing with ball milling (BM) were consolidated to disc-shaped samples with 10-mm diameter and 0.8-mm thickness at room temperature using high-pressure torsion (HPT). A relative density as high as 99.9 pct, high bending and tensile strengths of 2.55 to 3.45 and 1.35 GPa, respectively, and a moderate ductility of 8 pct with an ultrafine grained structure are achieved after cold consolidation with HPT, which exceed those of hot consolidation methods. X-ray diffraction (XRD) analysis showed that a phase transformation occurs from a phase to x phase during HPT under a pressure of 6 GPa as in bulk pure Ti, whereas no phase transformation is detected after processing with BM alone. It was confirmed that the strength and ductility are improved by a combined application of BM and HPT when compared with other severe plastic deformation methods applied to Ti and Ti-6 pct Al-4 pct V, so that no alloying elements are required for the achievement of a comparable strength and ductility.This study used high-purity Ti (99.5 pct) powders with a particle size less than 45 lm having impurities of O 0.35, C 0.02, N 0.03, H 0.02, Fe 0.03, Mn 0.005, Mg 0.02, Cl 0.04, and Si 0.01 (wt pct). The Ti powders were KAVEH EDALATI, Graduate Student, and ZENJI HORITA, Professor, are with the

Mechanical behavior and microstructure properties of titanium powder consolidated by high-pressure torsion

“…7 that this specimen showed enhanced plasticity of ~2.2%. In practice, this is lower than the plasticity of ~8% reported for the consolidated BM powder subjected to 10 whole revolutions [29]. It is worth noting that apparently during HPT straining to 10 revolutions the titanium underwent a reverse omega to alpha phase transformation which can increase the final ductility.…”

“…One way deserving special attention is to produce bulk nanostructured titanium through the cold consolidation of titanium powder by means of HPT. In order to significantly increase the strength, there is a report of ball-milled (BM) powder of Ti which was consolidated by HPT to form bulk nanocrystalline disks [29]. A relative high density (99.9%) and a high tensile strength were achieved after cold consolidation from ball-milled titanium powder and an additional sample was also consolidated from a non-BM Ti powder.…”

Application of High-Pressure Torsion to WC–Co Ceramic-Based Composites for Improvement of Consolidation, Microstructure and Hardness

“…Details concerning the phase transformations in Co were reported in a recent earlier paper. 33) It is noted that phase transformations were reported in several other materials such as Ti and Ti alloys, 20,34,35) Zr, 22,3638) Si, 2,39) TiNi 30) and ZrO 2 9) when processed by HPT. Second, a peak broadening occurs appreciably in WC through HPT when compared to HIP, indicating the occurrence of lattice strains, dislocations generation and grain fragmentation during the HPT processing.…”

Using Severe Plastic Deformation to Fabricate Strong Metal Matrix Composites

“…1 Processing by HPT is a most promising severe plastic deformation (SPD) technique producing true nanometer grains leading to and providing an excellent potential for achieving high hardness in most bulk metals. 2 In recent years, because of the introduction of intense plastic strain during processing, HPT has also been applied for the consolidation of metallic powders [3][4][5][6][7][8][9][10] and the bonding of machining chips 11,12 . There is, however, a saturation in the improved mechanical properties by grain refinement and further superior properties are not easy to obtain by processing directly on the alloy unless a subsequent SPD processing technique is applied on the processed material.…”