Mechanical properties of pure titanium and Ti-6Al-4V alloys with a new tailored nano/meso hybrid microstructure

Abstract

Pure titanium and Ti-6Al-4V alloy powders are treated by a mechanical milling process, which is one of the severe plastic deformation processes. The mechanical milling enables to produce a nano-grain microstructure very easily and has been applied to many powder materials. The bimodal microstructure in those mechanically milled powders is composed of a nano-grain structure with a grain size of about 50 nm in the surface-near region and of a work-hardened microstructure in the core region of the powder. We applied the hot roll sintering process to pure titanium and to Ti-6Al-4V mechanically milled powders. These compacts have a hybrid microstructure that consists of nano-grain structure with grain sizes of 200 to 500 nm and a micron size meso-grain structure. The hybrid microstructure materials demonstrate enhanced mechanical properties compared to conventional materials.

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

“…[41,46,[56][57][58] The published data include those after annealing, cold rolling, or hot rolling of bulk Ti [41,46] and of bulk Ti-6 pct Al-4 pct V, [41] HPT of bulk Ti under 2 and 6 GPa, [46] equal-channel angular pressing (ECAP) of bulk Ti for 8 passes, [56,57] ECAP followed by cold rolling or cold extrusion, [56,57] accumulative roll-bonding of bulk Ti for 8 passes, [58] and of BM followed by hot roll sintering of Ti powders. [41] Solid line represents a relation delineated through the points obtained by the annealed sample and conventional cold-rolled and hotrolled samples for bulk Ti. It should be noted that, as pointed out by Zhao et al, [59] care is required for this comparison, because the ratios of the gage length to the gage width are varied from 1 to 5.…”

“…11-Plots of ultimate tensile strength vs elongation to failure including published data for samples of pure Ti and Ti-6 pct Al-4 pct V after processing with different methods. [41,46,[56][57][58] We are also grateful to Professor H. Miura, Kyushu University, for lending us a facility of the density measurement. One of the authors (KE) thanks the Islamic Development Bank for a scholarship.…”

“…The ball-milled powders are then consolidated into bulk shapes using hot consolidation methods such as hot pressing, hot extrusion, hot isostatic pressing, hot roll sintering, spark plasma sintering, and spray forming followed by a sintering process. [33] In spite of various publications regarding the BM of Ti, [35][36][37][38][39][40][41][42] little attention has been paid to the cold consolidation of ball-milled Ti powders through the application of HPT.…”

Effect of bimodal grain size distribution on fatigue properties of Ti-6Al-4V alloy with harmonic structure under four-point bending

“…However, a homogeneous fine-grained structure formed by severe plastic deformation generally leads to a decrease in the ductility of metallic materials [3][4][5][6][7][8] due to the initiation of plastic instability in the early stage. Therefore, various microstructural designs have been proposed to improve both the strength and ductility of these materials [4][5][6][7][8][9][10][11][12][13][14][15][16].…”

“…For example, Morita et al [9] reported that the strength of Ti-6Al-4V alloy was improved by a short-time duplex heat treatment without a reduction in ductility. In particular, we have developed a harmonic structure design [12][13][14][15][16][17][18][19], which consists of a coarse-grained structure surrounded by a network structure of fine grains, using a powder metallurgy to improve both the strength and ductility of commercially pure titanium and Ti-6Al-4V alloy.…”