Sains Malaysiana 44(12)(2015): 1751–1756

Microstructural Evolution and High Strain Rate Mechanical Property

of Cobalt Superalloy Contain Titanium

(Evolusi Mikrostruktur dan Sifat Mekanik Kadar Terikan Tinggi

Superaloi Kobalt yang mengandungi Titanium)

TAO-HSING CHEN* & TING-YOU CHEN

Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, 807 Kaohsiung, Taiwan

Received: 29 September 2014/Accepted: 17 August 2015

ABSTRACT

The high strain rate properties and microstructure observations of cobalt base superalloyd contains 0.9% Ti were investigated using Hopkinson bar. These cobalt base superalloys are tested at strain rates of 2×103, 3×103 and 4×103 s-1 and at different temperatures (25, 500 and 900°C), respectively. It is found that the stress flow and strain rate sensitivity increases with increasing strain rate but decrease with increasing temperature. The microstructure observations confirm that the high strain rate mechanical behavior of the cobalt base superalloys specimens are directly related to the effects of the strain rate, temperature and the evolution of the microstructural texture. The strengthening mechanism in cobalt base superalloys is the multiplication of dislocation. The dislocation density increases with increasing strain rate but decrease with increasing temperature.

Keywords: Cobalt superalloy; dislocation; strain rate; Ti additions

ABSTRAK

Pemerhatian sifat kadar terikan yang tinggi dan mikrostruktur superaloi asas kobalt yang mengandungi 0.9% Ti dikaji dengan menggunakan bar Hopkinson. Superaloi berasaskan kobalt ini diuji pada kadar terikan 2 × 103, 3 × 103 dan 4 × 103 s-1 dan masing-masing pada suhu yang berbeza (25, 500 dan 900C). Adalah didapati bahawa kepekaan tegasan aliran dan kadar terikan meningkat dengan meningkatnya kadar terikan tetapi menurun dengan pertambahan suhu. Pemerhatian mikrostruktur mengesahkan bahawa kelakuan mekanik kadar terikan yang tinggi oleh spesimen superaloi berasaskan kobalt berkait rapat dengan kesan kadar terikan, suhu dan evolusi tekstur mikrostruktur. Mekanisme pengukuhan dalam superaloi berasaskan kobalt adalah pendaraban perkelehannya. Ketumpatan perkehelan meningkat dengan peningkatan kadar terikan tetapi berkurangan dengan pertambahan suhu.

Kata kunci: Kadar terikan; penambahan Ti; perkelehan; superaloi kobalt

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*Corresponding author; email: thchen@cc.kuas.edu.tw