Rapid Preparation,Micro-structure And Mechanical Properties Of W-Ni-Mn Alloy

Tungsten heavy alloys ?WHAs? possessing good comprehensive performance, are extensively applied in the national defense, military, aviation, electronic information and other fields. Militarily, the main materials used for kinetic energy penetrators are depleted uranium ?DU? and WHAs. Although DU warhead has better penetration depth, it can severely pollute the environment. The present WHA warheads commonly use the W-Ni-Fe alloys. However, the W-Ni-Fe alloys are not so sensitive to adiabatic shear band, and the warhead is easy to form the "mushroom head" in the armor-piercing process, thereby leading to the decrease in penetration capability. The new W-Ni-Mn alloys show better adiabatic shear performance and exhibit a self-sharpening performance in the armor-piercing process, thereby avoiding a decrease in the penetration depth. This is the reason why the W-Ni-Mn alloys can become the most promising potential substitute material for DU alloys. In this study, we focused on the preparation, microstructure and mechanical properties of the new fine-grained W-Ni-Mn alloys, and the main contents were as follows:Firstly, micron-sized W, Ni, and Mn powders were used as raw materials, and different pretreatment methods ?direct mixing, high-energy ball milling? were used in the raw materials. The effects of different pretreatment methods on W-Ni-Mn composite powders were studied in detail. The fine-grained 90W-6Ni-4Mn alloys were fabricated by using the pretreated composite powders via spark plasma sintering ?SPS?. The effects of SPS sintering temperature on the microstructure and mechanical properties of the 90W-6Ni-4Mn alloys were also investigated. Results showed that the particle size and dispersion of the composite powders pretreated by high-energy ball milling were smaller and more uniform. The fine-grained 90W-6Ni-4Mn alloys fabricated by using the high-energy ball milled powders, showed a uniform distribution and small average grain size, and exhibited excellent comprehensive mechanical properties.Secondly, based on the above research, to improve the mechanical properties of fine-grained WHAs,the "Two-stage sintering" was used to regulate the composition and microstructure of W-Ni-Mn alloys. Results showed that the 90W-6Ni-4Mn alloys fabricated by spark plasma two-stage sintering technology at 1100 ?, exhibited high densification of 96.65% and small average grain size of about 3.6 ?m. Compared with those of spark plasma liquid phase sintered alloys, the rockwell hardness of the two-stage sintered alloys increases, and the bending strength decreases slightly.The alloys possessing best comprehensive performance were obtained at 1100 ?, and its hardness and bending strength were 76.6 HRA and 785.30 MPa, respectively. The study of microstructure showed that the two-stage sintering promoted the sintering densification,and increased the average grain size ?the size was still relatively small?. The fracture modes were mainly W-W interface fracture and ductile tearing of the binding phase.Finally, the 90W-6Ni-4Mn-Y₂O₃ alloys were fabricated by using SPS technology at 1150 ?,and exhibited high densification of 96.3% and excellent comprehensive performance. The effects of the addition of trace rare earth oxide ?Y₂O₃? on the microstructure and mechanical properties of W-Ni-Mn alloy were studied. Results showed that the addition of trace Y₂O₃ inhibited the sintering densification process and refined the W grain size. With increasing the Y₂O₃ content, the average grain size of sintered alloys decreased obviously ?from 5.5 ?m to 2.1 ?m?. On the whole, the hardness of the alloys increased and the bending strength decreased with the addition of trace Y₂O₃. The best comprehensive mechanical properties of the alloys were obtained as the mass fraction of Y₂O₃ was 0.4%. The fracture modes of the alloys were mainly W-W interface fracture and W-binder interface fracture.