Thermal expansions and mechanical properties of electrodeposited Fe–Ni alloys in the Invar composition range

Significance Statement

Researchers from the Kyoto municipal institute of industrial technology and culture in Japan studied the mechanical properties and thermal expansion of electrodeposited Fe-Ni alloys in the invar composition range. The paper is now published in Electrochimica Acta.

Invar is also called nickel-iron alloy FeNi36 ­, it was discovered by Guillaume in 1897 with its application varying from optical and laser measuring system, bimetallic strips, shadow mask and storage vessels for liquefied natural gas among others. With the electrodeposition of the invar Fe-Ni alloys, a more precise processing and improve mechanical properties will be achieved. The novelty of the work is that invar electroforming process can provide free standing micrometer-sized 3 dimensional structures with good thermal dimension stabilities. Saccharin a stress reducer, is seen as indispensable when producing electrodeposited Fe-rich Fe-Ni alloys.

According to the research team, production of crack-free invar Fe-Ni alloy with 36 mass %Ni have been successful including its thermal properties and micro structure. As deposited invar alloys vary from unstable body centered cubic bcc phases or mixed bcc and face-centered cubic fcc phase. In contrast, pyrometallurgically produced invar alloys are mainly fcc phases.

The team pointed out that the introduction of heat, annealing at 6000C decreases the coefficient of thermal expansion CTE of electroformed invar metal mask to 3ppm/0C and it was found to be four times smaller than that of conventional Ni mask which was 13ppm/0C. Annealing of the invar alloy have been predicted to lead to strength degradation, this is due to grain coarsening, explained the research team.

Result shows that saccharin was added to reduce residual stress and improve roughness of electrodeposits. There was presence of 0.02 mass % of sulfur. The researcher later attributed the thermal contraction of invar Fe-36 mass% Ni alloy to an increase in the atomic packing density by the phase transformation from a bcc phase to an fcc phase. Considering the thermal contraction phenomena, the result obtained explained as-deposited invar Fe-36 to 40 mass% Ni alloys with CTE 2 to 10 times larger than those of pyrometallurgically produced Fe-Ni alloys were mainly composed of bcc phases. The ultimate tensile strength and hardness values of the electrodeposited Fe-80 mass% Ni alloy are higher than that of the as-deposited Fe-Ni alloys with 36 to 40 mass% Ni.

From the result, as-deposited invar alloys is seen to exhibit good ductility. Electrodeposited Ni and Ni-rich Fe-Ni alloys containing small amounts of sulfur are often embrittle annealing. Ductile behavior of the electrodeposited Invar Fe–Ni alloys was confirmed, irrespective of whether the alloys were heat-treated. Upon heat treatment at 400 to 5000C, the Invar Fe–Ni alloys exhibited high strength with good ductility, consistent with their low CTE. After the heat treatment, no severe embrittlement of the electrodeposited Invar alloys was observed despite the codeposition of sulfur because the sulfur existed as a granular sulfide, thereby preventing grain-boundary embrittlement.

The researchers were able to achieve an as-deposited invar Fe-Ni alloy which is of higher CTE than that of the existing pyrometallurgically produced invar alloy. A more precise processing and improved mechanical properties of the invar Fe-Ni alloys using electrodeposition was also achieved.

 

Thermal expansions and mechanical properties of electrodeposited Fe–Ni alloys in the Invar composition range. Advances in Engineering

 

About the author

Tomio Nagayama received the B.S. degree from Kansai University, Osaka, Japan, in 1994. 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 the B.S. and M.S. degrees from Ritsumeikan University, Kyoto, Japan, in 2007 and 2009, respectively. She is currently working as Associate 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 the 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. 

 

Journal Reference

Tomio Nagayama, Takayo Yamamoto, Toshihiro Nakamura.  Thermal expansions and mechanical properties of electrodeposited Fe–Ni alloys in the Invar composition range, Electrochimica Acta, Volume 205, 1 July 2016, Pages 178–187.

Kyoto Municipal Institute of Industrial Technology and Culture, 91 Chudoji Awata-cho, Shimogyo-ku, Kyoto 600-8815, Japan.

 

Go To Electrochimica Acta

 

 

Check Also

Computational Insights into High-Pressure Equilibria of Supercritical Gases in Ammonia - Advances in Engineering

Computational Insights into High-Pressure Equilibria of Supercritical Gases in Ammonia