Microstructure and dynamic mechanical properties of tungsten-based alloys in the form of extruded rods via microwave heating

https://doi.org/10.1016/j.ijrmhm.2013.08.003Get rights and content

Highlights

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    Large sized tungsten-based alloy extruded rods were achieved by microwave sintering.

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    Original microstructure evolution during dynamic compression.

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    Original formation of adiabatic shear bands during dynamic compression.

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    Excellent dynamic mechanical properties of microwave-sintered extruded rods.

Abstract

The dynamic mechanical properties of 93W–4.9Ni–2.1Fe alloys in the form of extruded rods sintered by microwave heating were investigated under dynamic compression using a split Hopkinson Pressure Bar. The microstructure and microhardness values of the sintered specimens after dynamic compression were analyzed and tested. The results show that the deformation amount and microhardness of specimens increase with increasing strain rate. When the strain rate is 3000 S− 1, the deformation amount is increased to the maximum value of 59.8%, and the microhardness values of the tungsten grains and the matrix phase are also promoted to the maximum values of 7.66 and 6.92 Gpa, respectively. The formation of cracks during compressive deformation initiates before the appearance of the adiabatic shear bands. As the strain rate increases, cracks initiating at the edge of specimens gradually propagate to the bulk alloy, and the adiabatic shear band is observed at about 45° to the loading direction under the strain rate of 3000 S− 1. These findings suggest that tungsten-based alloys extruded rods sintered by microwave heating would be an ideal material with excellent self-sharpening and penetration performance for penetrators.

Introduction

Tungsten-based alloys, possessing a series of excellent physical and mechanical properties, have a wide range of applications in the field of ordnance, especially used as the basic materials for kinetic energy penetrators [1], [2].When penetrators collide with targets, work hardening will occur because of the high-speed stamping and impacting. Additionally, the high melting point of the tungsten-based alloy slows down the trend towards thermal softening, thus, the strain hardening and strain rate hardening will go on, which will result in mushroom-like head and less adiabatic shear bands, leading to the poorer penetration performances [3], [4].

In order to promote the self-sharpening and penetration performances of tungsten-based alloys, researchers have undertaken considerable researches and found that refined grains could significantly optimize the microstructure of tungsten-based alloys so as to achieve the purpose of improving adiabatic shear sensitivity [5]. Microwave sintering, a kind of new sintering technology which can largely improve the mechanical properties of tungsten-based alloys, can effectively inhibit the growth of tungsten grains leading to a fine-grained microstructure during sintering [6], [7]. Meanwhile, powder extrusion molding is a novel near-net molding technology, which developed on the basis of the metal slab and polymer processing. Due to the advantages of high efficiency, the unlimited length of product and the uniform longitudinal density, powder extrusion molding has obtained great importance and has arrived to be a rapid development and application technology. But so far, the dynamic mechanical properties of the extruded tungsten-based alloy rods with large aspect ratio sintered by microwave have not been thoroughly investigated in the literature. Therefore, in this paper, the microstructure and dynamic mechanical properties of microwave sintered W–Ni–Fe alloy rods by extrusion will be investigated and corresponding self-sharpening potentiality will be discussed.

Section snippets

Experimental

Powder mixtures with a composition of 93W–4.9Ni–2.1Fe (wt.%) were first mixed in a cylinder mixer for 20 h, and then prepared for the extruding feed by adding an appropriate amount of binder. The characteristics of the tungsten, nickel and iron powders used in this study are summarized in Table 1. The extruded rods with a diameter of 24 mm were fabricated by a vacuum extruder (Dorst-V15, Germany). After solvent debinding and thermal debinding, the rods were sintered at 1550 °C for 30 min in a

Deformation amount

Fig. 3 shows the photo of specimens after testing under the dynamic compression rate of 1000, 2000 and 3000 S− 1 (from left to right, and original sample is in the leftmost). It can be seen from Fig. 3 that the deformation increases with the strain rate. In order to represent the degree of deformation, in this study, we introduce the formula of deformation amount, which can be expressed in the following:φ=S1−S0S0×100%where s0 and s1 are the areas of the surfaces perpendicular to the loading axial

Conclusion

The deformation amount of specimens increases with the enhancing of the strain rate. When the strain rate is 3000 S− 1, the deformation amount is increased to the maximum value of 59.8%. When the strain rates are 1000, 2000 and 3000 S− 1, the microhardness of tungsten grains are 6.62 GPa, 7.30 GPa, 7.66 GPa, and those of the matrix are 5.40 GPa, 6.00 GPa, 6.92 GPa, respectively. As the strain rate increases, the adiabatic shear bands are observed under the strain rate of 3000 S− 1, and cracks formed at the

Acknowledgments

The authors thank the National Natural Science Foundation of China (No. 50774098) and the Creative research group of the National Natural Science Foundation of China (Grant No. 50721003) for the financial support.

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