Densification, microstructure and mechanical properties of 90W-4Ni-6Mn heavy alloy

In the processing of W-Ni-Mn heavy alloys, the affinity of manganese to oxygen and the reduction of its oxides during sintering should be considered. In this work, an atmospheric controlling method was proposed to solve these problems. The sintering cycle consisted of a heating up to 600 degrees C in vacuum, holding after the atmosphere changed to an argon gas, and sintering at temperatures from 1050 to 1200 degrees C. Densities around 99.7% for the 90W-4Ni-6Mn alloys were obtained with sintering temperatures in the 1100-1200 degrees C range. Compared to the conventional heavy alloys, relatively lower temperature results in a finer grain size (6-10 mu m) after densification and consequently better performance in tensile test. A 1030 MPa ultimate tensile strength with a 25% elongation to failure was achieved when sintered at 1150 degrees C. Worth mentioning that grain coalescence plays as a typical coarsening mechanism in the case of the 90W-4Ni-6Mn alloy, and insufficient coalescence process could lead to a poor performance in elongation. These results show that by selecting a suitable sintering cycle, the 90W-4Ni-6Mn alloy with properties comparable to the W-Ni-Fe system can be obtained but with sintering temperatures 300 degrees C lower. (C) 2012 Elsevier Ltd. All rights reserved.