Abstract
Soft magnetic materials are characterized by achieving a high magnetic induction value in the presence of a small magnetic field. Common applications of these materials, such as transformers or sensors, are in constant evolution and new requirements are becoming more demanding. Nickel and its alloys are employed as smart materials taking advantage of their superior magnetoelastic properties. A metal injection molding (MIM) technique provides high-quality complex-shaped parts with a good density and controlled impurity levels, which are necessary for these applications, by carefully adjusting the sintering stage. Previous investigations have established a sintering cycle for pure nickel consisting of 1325 ∘C for 12 h within an N2-5%H2 atmosphere. Nevertheless, microstructural, mechanical and magnetoelastic responses can still be greatly enhanced. In this context, the effects of hot isostatic pressing (HIP), and sintering atmosphere have been investigated. The application of an adequate HIP treatment leads to significant improvements in comparison to the reference sintering process. It achieves almost complete densification while increasing field-dependent elastic modulus from 8.1% up to 9.6%. Additionally, the sintering atmosphere has been proven to be a key factor in reducing impurities and hence facilitating magnetic domain motion. Three different atmospheres have been studied: N2-5%H2 (with a higher gas flow), N2-10%H2-0.1%CH4 and low vacuum. Minimum carbon contents have been registered using more reducing atmospheres (N2-5%H2 and N2-10%H2-0.1%CH4) which has led to values of field-dependent elastic modulus higher than 10%. This value is 2.5 times higher than that obtained when nickel parts are processed via conventional techniques. Moreover, although minimizing carbon content has been shown to be easier and more beneficial than achieving complete densification, both strategies could be used in combination to improve and maximize magnetoelastic performance.
Highlights
Nickel-base materials are widely used for commercial purposes due to remarkable properties, reported extensively in the ASM Specialty Handbook [1], such as corrosion resistance, mechanical strength, thermal expansion, electrical conductivity, and magnetic properties
The feedstock was prepared by mixing the nickel powder with a previously developed multi-component binder system consisting of paraffin wax (PW) and high-density polyethylene (HDPE) in equal proportions
The effect of hot isostatic pressing has been studied on the sintered Metal Injection Moulding (MIM) parts with the objective of improving the magnetic performance of pure nickel parts processed by MIM
Summary
Nickel-base materials are widely used for commercial purposes due to remarkable properties, reported extensively in the ASM Specialty Handbook [1], such as corrosion resistance, mechanical strength, thermal expansion, electrical conductivity, and magnetic properties. Commercial products can be obtained in a wide range of shapes and sizes. Herranz [3] remarks that the processing of a high purity powder via the Metal Injection Moulding (MIM) technique provides contamination control and results in high-quality parts. Multiple purity grades of spherical or round carbonyl Ni powders with suitable particle size ranges for use in MIM are commercially available. MIM allows high production quantities of complex shapes, exceptional performance, and lower production costs than other manufacturing techniques
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