The Effect of Nickel to Manganese Ratio and the Matrix Phase on the Properties of W-Ni-Mn Tungsten Heavy Alloys

This research explored the impact of the nickel-to-manganese ratio and the influence of the matrix phase on the properties of W-Ni-Mn tungsten heavy alloys (WHAs), aiming to determine the optimal composition for achieving desirable alloy properties.  For this purpose, tungsten, nickel, and manganese powders with specified weight percentages underwent two rounds of wet milling.  Powder mixtures were obtained with weight ratios of ۹۰W-۶Ni-۴Mn, ۹۰W-۸Ni-۲Mn, and ۸۸W-۱۰Ni-۲Mn. These mixtures were then compressed through the cold pressing method at a pressure of ۲۵۰ MPa. Subsequent reduction and sintering processes were carried out in a tube furnace at temperatures of ۱۱۵۰ and ۱۴۰۰ °C, respectively. Microstructural characterization was conducted using both optical and electron microscopy. The results showed that the change in chemical composition is not significantly effective on the sintering density of the samples and also the highest sintering density, reaching ۹۰.۱۱%, was achieved with the ۸۸W-۱۰Ni-۲Mn sample. Furthermore, the results demonstrated that carburization of W-Ni-Mn WHAs during the sintering process led to an increase in the micro-hardness of the samples. The highest hardness, measuring ۳۸۱ Hv, was observed in the ۹۰W-۶Ni-۴Mn alloy, where carburization occurred. XRD results revealed that an increase in the nickel-to-manganese ratio led to a reduction in the peaks of manganese carbide and tungsten carbide. Consequently, this decrease in carbide peaks resulted in a reduction in hardness, reaching ۳۵۲ Hv in the case of the ۸۸W-۱۰Ni-۲Mn sample. Additionally, the alloys ۹۰W-۶Ni-۴Mn and ۸۸W-۱۰Ni-۲Mn both exhibited the lowest continuity, a value of ۰.۵. Fracture surface SEM images illustrated that the ۹۰W-۶Ni-۴Mn alloy, characterized by the lowest nickel-to-manganese ratio (۱.۵), exhibited the highest trans-granular fracture mode involving cleavage and matrix tearing, which is considered desirable. Furthermore, an increase in the matrix phase content resulted in a shift of the preferred crack path, originating from the matrix phase.

کلیدواژه ها:

Tungsten heavy alloys (WHAs) ، W-Ni-Mn ، nickel to manganese ratio ، liquid phase sintering (LPS) ، matrix phase