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.
Correlation between microstructure and properties of fine grained Mo–Mo3Si–Mo5SiB2 alloys
Abstract Three phase α-Mo–Mo 3 Si–Mo 5 SiB 2 alloys of various compositions, namely Mo–6Si–5B, Mo–9Si–8B, Mo–10Si–10B and Mo–13Si–12B (at.%) were processed by a powder metallurgical (PM) route. Increasing the Si and B concentration in these Mo–Si–B alloys resulted in increasing volume fractions of the intermetallic phases Mo 3 Si (A15) and Mo 5 SiB 2 (T2) and the distribution of the three phases present in these alloys was dependent on the volume fractions of the individual phases. Above volume fractions of about fifty percent, bcc Mo solid solution (α-Mo) formed the matrix. Consequently, Mo–6Si–5B and Mo–9Si–8B alloys, which possessed a continuous α-Mo matrix provided increased fracture toughness at ambient temperatures. Additionally, a decreased BDTT of about 950 °C is caused by the homogeneous α-Mo matrix. In contrast, Mo–13Si–12B with 65 vol.% of the intermetallic phases that formed the matrix phase in this material had a BDTT value higher than 1100 °C, while the strength at elevated temperatures up to 1300 °C was significantly increased compared to alloys that have the α-Mo matrix. Alloy compositions with ≥50 vol.% of intermetallic phases (corresponding to alloys containing a minimum of 9 at.% Si and 8 at.% B) were oxidation resistant with minimal mass loss under cyclic conditions for 150 h at 1100 °C due to the formation of a dense borosilicate glass layer that protects the material surface.
Microstructure and Wear Resistance of a Laser Melting-Deposited γ/NiMo Near-Eutectic Alloy
A γ/NiMo near-eutectic alloy mainly consisting of NiMo intermetallic compound and Ni-based solid solution γ was fabricated by laser melting deposition process using Ni-Mo elemental powder blends.Microstructure and room temperature dry sliding wear resistance of the alloy at different sliding speeds and test loads were studied.The alloy has a homogeneous microstructure and better wear resistance even at higher sliding speed and test load.Wear volume loss of the alloy is extremely insensitive to increasing wear test load at each sliding speed while coefficient of friction drastically decreases with the increase of both sliding speed and test load,what′s more,higher sliding speed brings lower wear volume loss and lower coefficient of friction,which is dominantly due to the combination of high hardness of the NiMo intermetallic compound and good toughness of the Ni-based solid solution γ.Wear volume loss of the alloy is only ten percent of that of hardened 0.45% C steel under the same testing condition of 0.93 m/s sliding speed and 196 N test load.