Microstructure and Tribological Properties of Mo–40Ni–13Si Multiphase Intermetallic Alloy
Intermetallic compounds are increasingly being expected to be utilized in tribological environments, but to date their implementation is hindered by insufficient ductility at low and medium temperatures. This paper presents a novel multiphase intermetallic alloy with the chemical composition of Mo–40Ni–13Si (at %). Microstructure characterization reveals that a certain amount of ductile Mo phases formed during the solidification process of a ternary Mo–Ni–Si molten alloy, which is beneficial to the improvement of ductility of intermetallic alloys. Tribological properties of the designed alloy—including wear resistance, friction coefficient, and metallic tribological compatibility—were evaluated under dry sliding wear test conditions at room temperature. Results suggest that the multiphase alloy possesses an excellent tribological property, which is attributed to unique microstructural features and thereby a good combination in hardness and ductility. The corresponding wear mechanism is explained by observing the worn surface, subsurface, and wear debris of the alloy, which was found to be soft abrasive wear.
Recent Advances in the Development of Mechanically Alloyed Mo Silicide Alloys
We review the current development status of Mo-Si-B alloys consisting of Mo solid solution and the intermetallic phases Mo3Si and Mo5SiB2 which could take advantage of the beneficial oxidation resistance of the silicide phases and of the outstanding mechanical properties of molybdenum. For adequate low temperature toughness a continuous Mo solid solution matrix should be established in the microstructure. Besides, wrought processing of such alloys at elevated temperatures requires the presence of an ultra-fine grained (UFG) microstructure. Both the prerequisites can be fulfilled using mechanical alloying (MA) as the crucial processing step which even yields nanostructured supersaturated powders after milling. However, values for the ductile-to-brittle transition temperature (DBTT) close to room temperature are unlikely due to grain boundary embrittlement by Si segregation. The possibility of reducing this segregation tendency by various micro-alloying additions will be demonstrated. Finally, the high temperature deformation behaviour of these UFG materials will be comparatively assessed against state-of-the-art Nickelbase single-crystalline superalloys.
Oxidation behavior of multiphase Mo–Si–B alloys
Abstract The oxidation behavior of multiphase Mo, Mo3Si, and Mo5SiB2 (T2) alloys was examined at 800 and 1300 °C. The alloys were cast and heat treated at 1600 °C before the cyclic oxidation tests were performed. The compositions of the alloys with Si/B ratios of 0.5, 0.71, and 1.0 were chosen near the L=(Mo)+T2 eutectic trough to produce a fine dispersion of the different phases. The multiphase alloys showed poor oxidation resistance at 800 °C while a protective glass scale formed at 1300 °C. At 800 °C the oxidation resistance improved as the volume fraction of the T2 phase increased. Conversely, at 1300 °C, the glass scaled that formed on the alloys with a Si/B ratio of 0.5 was not protective. However, a protective glass scale did form on the alloys with a higher Si/B ratio. The near eutectic alloy with a Si/B=1 was found to have the best oxidation resistance at 1300 °C. The results indicate the Mo3Si phase provides a source of silicon for controlling the composition of the glass scale at 1300 °C.