Effect of two-stage sintering process on microstructure and mechanical properties of ODS tungsten heavy alloy

Abstract

Oxide dispersion strengthened (ODS) tungsten heavy alloys have been considered as promising candidates for advanced kinetic energy penetrator due to their characteristic fracture mode compared to conventional tungsten heavy alloy. In order to obtain high relative density, the ODS tungsten heavy alloy needs to be sintered at higher temperature for longer time, however, induces growth of tungsten grains. Therefore, it is very difficult to obtain controlled microstructure of ODS tungsten heavy alloy having fine tungsten grains with full densification. In this study, two-stage sintering process, consisted of primary solid-state sintering and followed by secondary liquid phase sintering, was introduced for ODS tungsten heavy alloys. The mechanically alloyed 94W-4.56Ni-1.14Fe-0.3Y 2 O 3 powders are solid-state sintered at 1300-1450 • C for 1 h in hydrogen atmosphere, and followed by liquid phase sintering temperature at 1465-1485 • C for 0-60 min. The microstructure of ODS tungsten heavy alloys showed high relative density above 97%, with contiguous tungsten grains after primary solid-state sintering. The microstructure of solid-state sintered ODS tungsten heavy alloy was changed into spherical tungsten grains embedded in W-Ni-Fe matrix during secondary liquid phase sintering. The twostage sintered ODS tungsten heavy alloy from mechanically alloyed powders showed finer microstructure and higher mechanical properties than conventional liquid phase sintered alloy. The mechanical properties of ODS tungsten heavy alloys are dependent on the microstructural parameters such as tungsten grain size, matrix volume fraction and tungsten/tungsten contiguity, which can be controlled through the two-stage sintering process.

Dynamic deformation behavior of 93W-5.6Ni-1.4Fe heavy alloy prepared by spark plasma sintering

“…Ashby [33] has reported that under quasi-static loading, the yield strength of double-phase alloy is related to the inverse square root of average thickness of soft phase between hard phases because yielding of double-phase alloy begins by deformation of the soft phase. An adapted Hall-Petch relation for WHA was developed by Lee et al [17,18] by assuming deformation of WHA began with deformation of the soft matrix phase, as expressed by the following formula:…”

“…[13][14][15]. The second route is to add inhibitors (such as oxide dispersoids) to prevent grain growth [12,[16][17][18][19]. The last one is to adopt advanced fast sintering techniques such as microwave sintering [20][21][22] and spark plasma sintering (SPS) [23][24][25][26].…”

Effect of Yttrium Oxide Dispersion on the Microstructure and Properties of Tungsten Heavy Alloys

“…In order to avoid grain coarsening, a two-stage sintering cycle followed by heat treatment has been reported by Lee 8 ,et al to have a better control over the microstructure of ODS alloys. In two-stage sintering, solid state sintering (SSS) is carried out between 1300 °C and 1450 °C for 1 h -2 h and then subsequently liquid phase sintering (LPS) between 1465 °C and 1485 °C for 1 h. Solid state sintering results in near full density of the alloy while tungsten grain growth and contiguity can be controlled by using lesser holding time in the liquid phase sintering stage 8 . Densification upto 97 per cent can be achieved after solid state sintering but the microstructure will have contiguous tungsten grains and isolated matrix pools.…”

Effect of Cold Swaging on the Mechanical and Microstructure Characteristics of Tungsten Heavy Alloy

“…To enhance the mechanical and the ballistic characteristics of tungsten heavy alloys, there are several approaches, the first, by modifying the composition either by optimizing the proportions of tungsten and the other matrix ingredients (Ni, Fe, …etc.) or by Adding different types of oxides, like yttrium o xides [4][5][6], alu minum o xides [7] and zirconiu m oxides [4]. The second, by optimizing the processing parameters (co mpaction pressure, sintering temperature, time, and at mosphere).…”