(1. 中南大學(xué) 粉末冶金國(guó)家重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)沙 410083；
2. 中南大學(xué) 粉末冶金研究院，長(zhǎng)沙 410083)
摘 要: 對(duì)IN718鎳基高溫合金進(jìn)行溫度循環(huán)為350~650 ℃及不同應(yīng)變幅條件下的同相(IP)和反相(OP)熱機(jī)械疲勞試驗(yàn)；比較同相和反相的熱機(jī)械疲勞循環(huán)應(yīng)力響應(yīng)行為、滯后回線以及疲勞壽命；運(yùn)用金相顯微鏡、掃描電子顯微鏡對(duì)材料的微觀結(jié)構(gòu)以及斷口特征進(jìn)行分析。結(jié)果表明：IN718合金的熱機(jī)械疲勞應(yīng)力-應(yīng)變滯后回線最大拉應(yīng)力與壓應(yīng)力不對(duì)稱，表明合金在350~650 ℃范圍內(nèi)高溫時(shí)抵抗變形阻力較小；合金的循環(huán)應(yīng)力響應(yīng)行為在低應(yīng)變幅的同相熱機(jī)械疲勞的高溫半周呈現(xiàn)循環(huán)硬化現(xiàn)象，其余情況均為循環(huán)軟化現(xiàn)象；合金的同相熱機(jī)械疲勞壽命明顯低于反相熱機(jī)械疲勞壽命，合金熱機(jī)械疲勞壽命在應(yīng)變幅超過(guò)0.6%的條件下符合Coffin-Manson方程，在應(yīng)變幅0.4%的情況下實(shí)際疲勞壽命值偏高；IN718合金的同相熱機(jī)械疲勞的疲勞源處斷口為沿晶斷裂，反相熱機(jī)械疲勞的為穿晶斷裂，裂紋擴(kuò)展區(qū)和瞬斷區(qū)均為韌窩斷裂。
關(guān)鍵字: IN718鎳基高溫合金；熱機(jī)械疲勞；同相；反相；疲勞壽命；斷口
（1. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China;
2. Powder Metallurgy Research Institute, Central South University, Changsha 410083, China）
Abstract:This research focuses on the thermomechanical fatigue (TMF) performance of IN718 superalloy upon in-phase (IP) and out-of-phase (OP) loading modes, respectively. The differences of strain response, hysteresis loop and fatigue life between IP and OP were compared. The hysteresis loop curves show that the stresses are not symmetric during tension and compression loading, and exhibiting relatively low deformation resistance at high temperature. In most cases, the stress exhibits cyclic softening behavior, only while at the IP TMF fatigue and upon low strain amplitude, the stress displays cyclic hardening behavior in the high temperature half cycles. The S-N curves show that the fatigue life upon out-of-phase mode exceeds that of in-phase process. The S-N plots are in accordance with the Coffin-Manson formula for the strain range over 0.6%, while it is not true below strain range of 0.4%. The microscopic examination shows that intergranular fracture dominates the deformation process for the in-phase TMF, which is contrast with the intragranular fracture for the out-of-phase counterparts. The dimples can be ubiquitously observed for these two fatigue modes.
Key words: IN718 superalloy; thermomechanical fatigue; in-phase; out-of-phase; fatigue life; fracture
