Recent development trends in metal forming

Due to the intrinsic properties of tungsten, such as high melting point and high thermal conductivity, selective laser melting of pure W parts experiences many challenges. In this study, the effects of volumetric energy density on the densification behavior, microstructure evolution and mechanical performances of SLM-processed pure tungsten parts were investigated. A maximum density of 19.0 g/cm3 (98.4% of the theoretical density) was obtained at the optimal energy density of 1000 J/mm3 and its microstructure was free of pores and balling phenomenon. The formation mechanism of pores and cracks was systematically investigated. The microhardness and compressive strength of SLM-processed pure W parts reached 474 HV and 902 MPa, respectively, which were comparable to the samples produced by conventional manufacturing methods. The morphology of fracture demonstrated that the fracture mechanism of SLM-processed pure W parts was brittle fracture and intergranular fracture was the main fracture mode. Dry sliding wear tests showed that the wear mechanism changed with the energy density. For pure W parts processed by SLM at the optimal parameters, the adhesion of hardened tribolayers was formed. In this case, the reduced coefficient of friction (COF) of 0.45 and a low wear rate of 1.3 × 10−5 mm3·N−1·m−1 were obtained.

Selective laser melting additive manufacturing of pure tungsten: Role of volumetric energy density on densification, microstructure and mechanical properties

In this paper, biodegradable low elastic Mg-Zn-Mn-Si-HA alloys have been synthesized by element-alloying assisted spark plasma sintering (SPS) process. The main concern of the current investigation...

Bio-inspired low elastic biodegradable Mg-Zn-Mn-Si-HA alloy fabricated by spark plasma sintering

Three types of scanning strategies, including the chessboard scanning strategy, the zigzag scanning strategy and the remelting scanning strategy, were conducted to study the effects of scanning strategies on surface morphology, microstructure, mechanical properties and the grain orientation of selective laser melted pure tungsten. The results showed that the pores and cracks were main defects in SLM-processed tungsten parts. The pores could be eliminated using the remelting scanning strategy. However, the cracks seemed to be inevitable regardless of the applied scanning strategies. The microstructures of SLM-processed tungsten were columnar grains and showed strong epitaxial growth along the building direction. A compressive strength of 923 MPa with an elongation of 7.7% was obtained when the zigzag scanning strategy was applied, which was the highest among the three scanning strategies. By changing the scanning strategies, the texture of SLM-processed tungsten in the direction of processing could be changed.

https://iopscience.iop.org/article/10.1088/2631-7990/ab7b00/pdf

Effects of laser scanning strategies on selective laser melting of pure tungsten

The effects of cold and warm rotary swaging and subsequent post-process annealing on mechanical properties, residual stress, and structure development within WNiCo powder-based pseudo-alloy were predicted numerically and investigated experimentally. The swaging temperature of 900 °C imparted increase in the Young’s and shear moduli; the post-process annealing at 900 °C also imparted decrease in the residual stress values, primarily due to structure recovery introduced within the matrix. Cold rotary swaging at 20 °C imparted ultimate tensile strength of almost 1 900 MPa, while warm rotary swaging at 900 °C introduced increased plasticity (almost 24 % after a single swaging pass). Post-process heat treatment promoted diffusion of W to the Ni/Co matrix, which increased strength, but remarkably decreased elongation to failure and residual stress. Numerically predicted results of mechanical behaviour corresponded to the experimental results and confirmed the favourable effects of the selected thermomechanical treatments on WNiCo performance.

Effect of thermomechanical processing via rotary swaging on properties and residual stress within tungsten heavy alloy

The effect of cobalt (0.5 wt%, 1.0 wt%, 1.5 wt% and 2.0 wt%), as an alloying element, on the microstructure and mechanical properties of W-Ni-Fe tungsten heavy alloy (WNF) prepared through spark plasma sintering (SPS) process is investigated in this work. The sintering is performed at 1400 °C with a heating rate of 100 °C/min and holding time for a period of 2 min. The properties of the cobalt added heavy alloys (WNFC) are found to be superior to that of the tungsten heavy alloy without cobalt addition. The 1.0% cobalt alloy is observed to give higher yield and tensile strengths compared to other alloys. As the mechanical properties of the alloys depend on the microstructural features, a detailed study on the influence of the microstructural parameters such as average grain size, contiguity and matrix volume fraction on the properties of the alloys is carried out. The average tungsten grain size of WNF alloy is 12.3 µm and that of WNFC alloys is from 9.5µm to 11.5 µm. The control of grain size is significantly evident in the case of spark plasma sintered alloys. The yield strength is found to be influenced by the W-grain size of the microstructure. The contiguity of the WNFC alloys is observed to decrease with increase in percentage of cobalt addition. The fractograph analysis of the tensile tested specimen helps in understanding the tensile behaviour of the alloys. The WNFC alloys show predominantly W-grain cleavage fracture compared to the WNF alloy, possibly due to the good cohesive strength of the matrix phase and W/matrix interface, because of cobalt addition and also due to the high heating rate followed in the SPS process.

Microstructure and mechanical properties of spark plasma sintered tungsten heavy alloys

Tungsten is a refractory metal possessing good mechanical properties of high strength, high yield point, and high resistance to creep. Therefore, tungsten and its alloys are used in many high temperature applications. Due to the high melting point, they are generally processed through powder metallurgy method. The powders are compacted using die pressing or isostatic pressing. The compacts are sintered in a sintering furnace to achieve high density, thereby, making the metal suitable for further processing. This article reviews the recent research findings of consolidating tungsten and its alloys (W–Ni–Fe and W–Ni–Cu), from preparation of powder alloys to sintering of the compact. The advances in sintering are based on the objective of achieving good densification of the metal at lower temperature and at faster rate. The use of microwave sintering and spark plasma sintering techniques resulted in significant reduction in sintering time and producing products of good mechanical properties.

Sintering of Tungsten and Tungsten Heavy Alloys of W–Ni–Fe and W–Ni–Cu: A Review

The sintering temperature of pure tungsten can be reduced through the addition of small amounts of transition elements The present study deals with the activated sintering of tungsten with 10 wt%

N. Senthilnathan

Papers

Microstructure and mechanical properties of spark plasma sintered tungsten heavy alloys

Sintering of Tungsten and Tungsten Heavy Alloys of W–Ni–Fe and W–Ni–Cu: A Review

Activated sintering of tungsten alloys through conventional and spark plasma sintering process

Synthesis of tungsten through spark plasma and conventional sintering processes

A Two Stage Finite Element Analysis of Electromagnetic Forming of Perforated Aluminium Sheet Metals