Influence of powder characteristics on sintering behaviour and properties of PM Ti alloys produced from prealloyed powder and master alloy

Abstract

Abstract:The use and development of titanium and titanium alloys have been strongly correlated to high technology industries where costs are not the most important aspect. Titanium could see its market grow by the application of lower cost and more efficient processing methods such as powder metallurgy. This work deals with the characterisation of two types of powders: commercial prealloyed powder and powder produced from master alloy combining mechanical milling and conventional blending to adjust the particle size. The characteristics of the powders, sintering behaviour and final properties of the parts indicate that the master alloy approach leads to better compressibility than the prealloyed powders and, therefore, to lower dimensional change during sintering. The most important result is that it is possible to obtain Ti alloys with properties similar to or better than alloys from prealloyed powders and to obtain homogeneous microstructures, which allows the composition to be adjusted

Inductive hot-pressing of titanium and titanium alloy powders

“…2, it can be seen that in most cases it is possible to produce fully dense materials. With only two of the alloys, Ti-3Al-2.5V from prealloyed powder and Ti-6Al-7Nb, fully dense materials were not obtained; however, even in the worst case, the relative density is higher than 97%, which is greater that the values normally attained with conventional PM for titanium [25]. Hot-pressing has been found to be particularly advantageous for forming parts from prealloyed powders [17]; however, from the relative densities shown in Fig.…”

“…The titanium alloy powders processed were either purchased (the hydride powder and prealloyed powders) or produced by combining high-energy milling (HEM) and conventional blending; the details of the production and characterization of the Ti-6Al-4V and Ti-3Al-2.5V powders can be found elsewhere [25]. To produce the Ti-6Al-7Nb alloy, an HDH titanium powder and a Nb/Al/Ti (65:35:5) master alloy with particle size lower than 0.8 mm (20 mesh) were used.…”

Mechanical behaviour of pressed and sintered titanium alloys obtained from master alloy addition powders

“…Some characteristics of the starting powders provided by the supplier are reported in Table 1. The acquired Al:V (35:65) master alloy was milled in combination with the elemental titanium to reduce the particle size and adjust the composition with elemental aluminium purchased by Sulzer Metco Ltd. The optimised Al:V master alloy has the correct ratio of alloying elements (60:40) and a particle size lower than 63 μm (Bolzoni et al, 2011) and was, therefore, blended with elemental titanium in a "turbula" mixer during 30 minutes to obtained the Ti-6Al-4V and Ti-3Al-2.5V alloys. Firstly, the characterisation of the titanium alloy powders was done in terms of differential thermal analysis (DTA), dilatometry and X-ray diffraction (XRD).…”

Role of stabilisers in the design of Ti aqueous suspensions for pressure slip casting

“…This strategy would provide better control of the mechanical properties, as well as modification of the elastic modulus and improvement of the wear resistance, as demonstrated Bolzoni et al [7].…”

“…Those high sintering temperatures and times increase the grain growth and the content of interstitial elements (such as oxygen and nitrogen), which are detrimental to mechanical properties [6]. Those problems could be overcome by reducing the particle size of the starting powders and consequently the sintering temperature, but the use of fine particles makes the pressing step more difficult if uniaxial pressing is to be used [7]. Another strategy to avoid grain growth during sintering, in addition to reducing the sintering temperature, is the addition of small percentage of submicron or nanometric ceramic particles, such as Al2O3, ZrO2 or Y2O3, to fix grain boundaries by particle pinning or by solution drag, as described by Manohar et al [8].…”