Effect of Applying Hot Isostatic Pressing on the Microstructure and Mechanical Properties of Tungsten Heavy Alloys

Document Type : Original Article


Egyptian Armed Forces, Egypt.


Abstract: The objective of this experimental study is to investigate the effect of hot isostatic pressing (HIP) on the density, mechanical properties and microstructure of pre-sintered specimens of 93%W-4.9%Ni-2.1%Fe alloy. To achieve this target, Containerless HIPing at temperature 1300°C was applied. While, the HIPing pressure was varied from 100 MPa to 150 MPa.
Elemental powders were mixed using double cone mixer for 2 hours. Cold Isostatic Pressing was applied for consolidation of metal powders into green compacts to obtain cylindrical tensile and impact specimens at 200MPa using rubber molds. Finally, the specimens were sintered under vacuum atmosphere at 1470ºC for 30 minutes. The applied HIPing temperature was chosen to be 1300°C. While, the applied HIPing pressure was varied from 100MPa to 150MPa, in order to study the effect of HIPing pressure on the mechanical properties, and the soaking time was 60 minutes.
The effect of applying Hot Isostatic Pressing was characterized in terms of density, hardness, impact resistance and tensile properties, then compared with samples in the as sintered state.
The microstructure analysis indicates that connectivity, contiguity and average grain size increase, while micropores were almost eliminated, this took place when applying a HIPing cycle at 1300°C under 100MPa for 60 minutes. On the other hand, When the HIPing pressure was increased to 150 MPa, a severe plastic deformation of the tungsten grains takes place, contiguity seriously increases leading to inhomogeneous microstructure.
The tensile strength and hardness increase when applying hot isostatic pressing of 100MPa, compared with its value in the as sintered state, Further increase in HIPing pressure up to 150MPa decreases theses values of strength and hardness, relative to its value at 100MPa. On the contrary, ductility and impact resistance decrease continuously when applying a HIPing cycles under 100MPa and 150MPa respectively, relative to its value in the as sintered state.