Add Cobalt And Manganese And Sintering Of 95w Alloy Mechanical Properties

Tungsten heavy alloys (WHAs) are of a group of tungsten based materials with additions of Ni and other elements such as Fe, Cu, Co, Mn, etc. Due to their combination of high density, high strength and good ductility, WHAs have a wide usage such as kinetic energy penetrators instead of depleted uranium alloys. In order to reach a high penetration capability, WHAs must have both high strength and high ductility.In this study, the 95W-Ni-Fe-Me series alloys (Me stands for Co, Mn or other alloying elements) are prepared by powder metallurgical (PM)methods. The PM process consists of four steps of mixing, CIP, hydrogen sintering, and vacuum heat treatment. The mechanical properties are examined by material testing machine, the tungsten grain size is determined by optical microscopy, the microstructure and fractograph are studied by SEM, the elemental composition of microzone is studied by EDS, and the phase composition is tested by XRD. Effects of the amount of Co, Mn and the technique of sintering and heat treatment on the microstructure and the mechanical properties of 95W alloys are studied, and the research results are as follows:High quality 95W alloys can be prepared by the process of hydrogen sintering followed by vacuum heat treatment. Most of the impurity element, oxygen segregates on the edge of crystalline grains of tungsten and the surface of remained apertures, and apertures can be formed easily at which the oxide is gathered. The atom diffusion of Fe, Ni, Co and the sintering kinetic force are influenced by oxygen. Hydrogen sintering process can be used to eliminate the influence of oxygen on the microstructure of 95W alloys and increase their mechanical properties. Following the hydrogen sintering process, 95W alloys samples shall be heat treated in vacuum to reduce the amount of remained hydrogen and the tendency of hydrogen brittlement, eliminate the element aggregation on the boundaries of tungsten grains, lessen the residual stress on the surface of the machined 95W alloys samples, and improve their mechanical properties.The addition of Co can both improve the strength and ductility of the 95W-Ni-Fe alloy at the same time. 95W alloys with moderate mechanical properties can also be obtained with the process of low temperature sintering by the addition of Mn in the alloys. However, if we want to get 95W alloys with high density, high tensile strength and high elongation, we should choose Co not Mn as a addition element and sinter the alloy at higher temperature. Because, the apertures tend to forming at high temperature when the Mn element is added in 95W alloys.With the sintering temperature increasing, tungsten grain size becomes larger, and the matrix phase tends to distributing between tungsten grains from partial aggregation form to web one, which will reduce the contact degree of W/W grain, and improve the mechanical properties of 95W alloys.The high performance 95W-3.15Ni-l.35Fe-0.5Co alloy, with density of above 18 g/cm3, tensile strength of above 980 MPa and elongation of above 28%, can be obtained by the process of sintering at 1540°C for about one hour in hydrogen atmosphere followed by vacuum heat treatment at 1200°C for about 5 hours.