微觀組織結構與小負荷維氏硬度
( 1. 中南大學 粉末冶金國家重點實驗室， 長沙 410083；
2. 長沙礦冶研究院， 長沙 410012；
3. 中南大學 冶金科學與工程學院， 長沙 410083)
摘 要: 用光學顯微鏡觀察了采用兩步法工藝制備的雙相結構功能梯度WC-Co硬質(zhì)合金的微觀組織結構，并測量了其小負荷維氏硬度。 結果表明： 合金芯部的η相呈點狀彌散分布于硬質(zhì)相WC顆粒之間和硬質(zhì)相WC顆粒與Co粘結相之間； 在3相區(qū)，由于超細η相的存在， WC晶粒大部分已失去其多角特征， 出現(xiàn)晶粒圓化現(xiàn)象； DP合金前驅體在后續(xù)滲碳處理過程中， 合金表層的部分Co在碳勢差的作用下向合金內(nèi)部發(fā)生遷移，使合金中間過渡層及其附近區(qū)域中Co粘結相呈現(xiàn)梯度變化； 合金表層與合金中間過渡層在由原來的3相組織變?yōu)閮上嘟M織的同時， 合金中細小的WC晶粒明顯減少， WC晶粒的均勻度明顯增加； 合金截面的小負荷維氏硬度出現(xiàn)由高變低再由低變高的規(guī)律性變化， 與合金內(nèi)部微觀組織結構的變化相對應。
關鍵字: 硬質(zhì)合金； 雙相結構； 功能梯度合金； 微觀組織； 維氏硬度
ZHANG Chuan-fu3
（ 1. State Key Laboratory of Powder Metallurgy,
Central South University, Changsha 410083, China;
2. Changsha Mining and Metallurgy Research Institute, Changsha 410012, China;
3. School of Metallurgical Science and Engineering,
Central South University, Changsha 410083, China）
Abstract: The microstructure of functionally graded WC-Co cemented carbide with dual phase structure prepared by so-called two-step technique was observed by metallography. Vickers hardness (HV2) along the gradient was tested by micro-hardness tester. The results show that the η phase in the core zone is in dispersion-distributed state, locating between WC and WC particles, and between WC particle and the binder with an average grain size less than that of WC. Because of the existence of fine η phase, most of the WC grains in the core zone loss their multi-angle character, taking a rounded appearance. During the carbonization process of the as-sintered cemented carbide with η phase in the whole body, part of cobalt in the surface zone migrates towards the inner of the alloy under the driving force of carbon-activity difference, with the formation of cobalt gradient structure and the microstructure change of the surface zone and the intermediate zone from the original WC+γ+η into WC+γ, accompanied by the remarked decrease of very small WC grains and the increase of uniformity degree of WC grains. Vickers hardness (HV2) along the gradient changes regularly from high to low, then from low to high, corresponding to the microstructure change in the alloy.
Key words: cemented carbide; dual phase structure; functionally graded material; microstructure; vickers hardness
