Effect of Processing Parameters on the Mechanical and Structure Properties of 93W–4.9Ni–2.1Fe Tungsten Heavy Alloy

Abstract

The objective of this experimental study is to investigate the effect of the main compaction and sintering parameters on the micro-structure and the mechanical properties of the liquid phase sintered 93%wt.W-4.9%wt.Ni-2.1%wt.Fe tungsten heavy alloy aiming at determining the optimum values of these parameters. Elemental powders were mixed using planetary mixer for 5 hours to ensure suitable homogeneity. Uni-axial compaction was applied to obtain standard tensile and impact specimens using compaction pressures ranging from 50MPa to 300MPa. Vacuum liquid phase sintering was carried out under different temperatures from 1460 ᵒ C up to 1500 ᵒ C and sintering time from 30 minutes up to 120 minutes. The effect of these parameters was characterized in terms of density, hardness, impact resistance and tensile properties. Microstructure variations, notably grain size, matrix volume fraction and contiguity were measured and used to explain the effect of sintering temperature and time on the properties. The obtained results indicated that optimum hardness and impact resistance can be obtained at a compaction pressure of about 200 MPa. As the sintering temperature increases, the grain size and volume fraction of matrix increase, while the contiguity decreases. As a result of these micro-structural changes, strength and hardness decrease. On the other hand, ductility and impact resistance increase with sintering temperature to some maximum at 1480 ᵒ C. At further increase of this temperature, grain growth becomes the dominant factor leading to a sensible decrease in all properties. The effect of sintering time on mechanical properties is related to grain growth and pore coarsening mechanisms. It is generally observed that strength and ductility decrease after sintering over 90 minutes at 1480 ᵒ C. It was also noticed that the ductility is more sensitive to sintering time and is reduced sharply with prolonged holding at the sintering temperature. It can be concluded that the mechanical properties of tungsten heavy alloys are sensitive to the processing cycle and are adversely affected by residual porosity. Moreover, tungsten grain size plays an important role in dictating the failure mode during tensile testing. If tungsten grain size is large interface failure is predominant. However, as the grain size decreases, fracture mode changes gradually from interface failure to matrix failure and then to tungsten grain cleavage failure.

Effect of Alloy Composition on the Mechanical Properties and Fracture Behavior of Tungsten Heavy Alloys

“…Sintering temperature was varied from 1470°C up to 1530°C for a period of 90 minutes in accordance with the sintering cycle applied in [11]. (c)…”

“…The samples with different compositions were tested in the as-sintered condition in an identical procedure explained in [11], and the following properties were determined.…”

Phases Identification by X- Ray Analysis for Liquid Phase Sintered Tungsten Heavy Alloys

“…The effects of sintering temperature on mechanical properties are essentially attributed to the resulting variations in grain size, matrix volume fraction and contiguity [9], the later defines the contiguity of tungsten grains in tungsten alloy defined as the relative fraction of tungsten-tungsten interfacial area.…”

“…X-ray diffraction pattern obtained using tungsten heavy alloy having the composition 91%W-6%Ni -3%Co uni-axially compacted under 200 MPa and sintered for 90 minutes at 1510°C.The obtained diffraction peaks and their corresponding position 2θ obtained for W-Ni-Co based heavy alloy together with their relative intensities are shown in Table(9).…”