EFFECT OF HEAT TREATMENT ON THE MECHANICAL PROPERTIES AND FRACTURE BEHAVIOR OF TUNGSTEN HEAVY ALLOYS

R.Osama, A.S.Abdallah, A.Fayed, G.M.Abdo, M.T.Sallam

Abstract: The objective of this experimental study is to investigate the effect of heat treatment on the mechanical properties and the fracture behavior of the liquid phase sintered (LPS) tungsten heavy alloys. For this purpose, tungsten alloy with three different compositions 93%W-4.9%Ni-2.1% Fe, 91%W-6%Ni-3%Co and 90.5%W-5.6%Ni-1.4%Fe-1.5%Co were prepared by conventional powder metallurgy route. Elemental powders were mixed using planetary mixer for 5 hours to ensure suitable homogeneity. Uni-axial compaction pressure of 200 MPa was applied to obtain standard tensile and impact specimens. Vacuum liquid phase sintering was carried out at 1500?C for 60 minutes. The sintered specimens were then heat treated, at 1100°C for 60 min, in an atmosphere of dynamic argon gas, and then water quenched. The effect of this heat treatment was characterized in terms of hardness, impact resistance and tensile properties and compared to those properties for samples in the as sintered state. The application of the prescribed heat treatment on these heavy alloys with the adopted chemical compositions provided a remarkable improvements in the mechanical properties. The tensile fracture behavior of these alloys with was studied. By scanning electron microscope, the obtained micrographs of the fractured surfaces showed that, by the application of the prescribed heat treatment, the fracture modes changed from brittle intergranular separations to matrix failure and tungsten cleavage which corresponds to a net improvement in mechanical properties, especially in the alloys where cobalt is added to the matrix constitution. This can be attributed to the increase in tungsten-matrix interfacial strength by the dissolution and of brittle intermetallic phases. It can be concluded that tungsten heavy alloys, particularly when cobalt is added as an alloying element should be used in the heat treated state. The effect of heat treatment is thus attributed to the dissolution of the brittle phases that may form on the M/W interface.

Keywords: Tungsten Heavy Alloy, Heat Treatment, Intermetallics, Interfacial Strength.

DOI: https://doi.org/10.15623/ijret.2017.0601026