Properties of electrodeposited invar Fe–Ni alloy/SiC composite film

Significance 

Invar alloys can be defined as iron-nickel alloys having 30-40% by mass of nickel in their composition. Recent studies have shown that the coefficient of thermal expansion at room temperature for these type of alloys changes significantly depending on the alloy composition. To be precise, iron-nickel alloys with 36% mass of nickel exhibit the lowest coefficient of thermal expansion. This alloys can be fabricated through invar iron-nickel alloy electroforming process (KEEPNEX™). Unfortunately, the strength of the electrodeposited invar alloy films decreases during heat treatment at 600° C due to grain growth. The need to improve the mechanical properties of the electrodeposited invar alloy films after heat treatment has triggered further research. More so, their potential applicability as micro/nano-molds in micro-electromechanical systems is quite motivating owing to their low coefficient of thermal expansion. Surprisingly, most of the available literature on composite electroplating uses only nickel or nickel rich alloys, therefore, little has been done on composite plating using the Invar iron-nickel alloys as the metal matrix.

Kyoto Municipal Institute of Industrial Technology and Culture researchers, Tomio Nagayama and colleagues developed fabricating electrodeposited Invar iron–nickel alloy/Silicon carbide composite films where silicon carbide was used as the hardening fine particle. They hoped to investigate the properties of the electrodeposited composite films correlated to their microstructure, and elucidate on the role of the co-deposited particles and the heat treatment to obtain electrodeposited films of high hardness and low coefficient of thermal expansion. Their work is now published in the research journal, Surface & Coatings Technology.

Briefly, the team begun by adopting modified based Watt-type nickel plating bath to prepare the iron-nickel bath. They then applied the composite electroplating method to electrodeposit invar iron-nickel composite films. Eventually, the research team assessed the composite films and correlated them to their microstructure.

The authors were able to obtain Invar iron–35-37% by mass nickel alloy/Silicon carbide composite films with the silicon carbide contents up to 20.8% by volume. The team observed that the co-deposition of silicon carbide particles increased the hardness of the electrodeposited films and suppressed the decrease in hardness by the heat treatment at 600° C. To be precise, they noted that the hardness of the films with around 20% by volume of silicon carbide remained almost unchanged after the heat treatment, and was comparable to that of the as-deposited Invar alloys without silicon carbide and higher than that of pyrometallurgically produced Invar alloys.

Tomio Nagayama and colleagues have successfully fabricated electrodeposited invar iron-nickel alloy/Silicon carbide composite films and assessed the effects of heat treatment in a bid to improve the mechanical properties of the electrodeposited invar alloy films. It has been seen that the heat treatment reduces the coefficient of thermal expansion of the composite film as with the electrodeposited invar iron-nickel alloy. The results are positive and have shown that the composite films can be used in the fabrication of microelectromechanical systems elements which require high mechanical strength and high thermal dimensional stability.

Properties of electrodeposited invar Fe–Ni alloySiC composite film. Advances in Engineering

Figure legend: Backscattered electron images of the cross section of the electrodeposited Invar Fe–36 mass% Ni alloy films and the electrodeposited Invar Fe–35 mass% Ni alloy/SiC composites before and after heat treatment at 600°C. Arrows show film growth direction.

About the author

Dr. Tomio Nagayama received his B.S. degree from Kansai University, Osaka, Japan, in 1994, and received his Ph.D. degree in Engineering from Nara Institute of Science and Technology (NAIST), Nara, Japan, in 2017. He is currently working as Chief Researcher at the Surface Finishing Technology Lab., Kyoto Municipal Institute of Industrial Technology and Culture.

His current research is focused on the development of new metals and alloys as functional materials using electrochemical processes for industrial applications, particularly, the manufacture of Micro-Electro-Mechanical Systems (MEMS) and flat panel displays (FPD) including Organic light-emitting diodes (OLED).

About the author

Takayo Yamamoto received her B.S. and M.S. degrees from Ritsumeikan University, Kyoto, Japan, in 2007 and 2009, respectively. She is currently working as Senior Researcher at the Surface Finishing Technology Lab., Kyoto Municipal Institute of Industrial Technology and Culture.
Main topics of activity: Electroanalytical chemistry, electroless plating and electroforming of metals and alloys for the manufacture of precision industrial parts.

About the author

Toshihiro Nakamura received his B.S. degree from Ritsumeikan University, Kyoto, Japan, in 1994. He is currently working as Chief Researcher at the Surface Finishing Technology Lab., Kyoto Municipal Institute of Industrial Technology and Culture.
Main topics of activity: Analytical chemistry and electrochemistry, electroplating and electroforming of metals and alloys, nanomaterials for micro electro devices, corrosion and corrosion control.

Reference

Tomio Nagayama, Takayo Yamamoto, Toshihiro Nakamura, Yutaka Fujiwara. Properties of electrodeposited invar Fe–Ni alloy/SiC composite film. Surface & Coatings Technology volume 322 (2017) pages 70–75.

 

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