【摘要】：鈦合金是20世紀50年代開發(fā)的一種輕質合金,因其在力學性能、耐蝕性能、耐熱性能等方面的優(yōu)異表現,逐漸成為工程應用上重要的結構材料。其中,亞穩(wěn)β鈦合金以其較高的強度、韌性以及優(yōu)良的冷加工性能,近年來日益受到人們的關注。作為一種結構材料,亞穩(wěn)β鈦合金常被應用于機械結構關鍵部位,疲勞失效是其主要的破壞形式之一。然而,針對亞穩(wěn)β鈦合金的研究主要集中于顯微組織、基本力學性能等方面,關于Ti-3Al-8V-6Cr-4Mo-4Zr合金的疲勞性能以及疲勞變形中顯微結構變化的研究很少見。本論文采用金相顯微鏡(OM)、掃描電鏡(SEM)、透射電鏡(TEM)等手段對不同熱處理狀態(tài)下Ti-3Al-8V-6Cr-4Mo-4Zr合金的顯微組織、拉伸性能以及低周疲勞性能進行了系統(tǒng)的研究,分析了熱處理工藝對合金微觀組織的影響,討論了不同狀態(tài)下合金拉伸、疲勞變形行為及損傷機制。研究發(fā)現:熱軋態(tài)Ti-3Al-8V-6Cr-4Mo-4Zr合金的顯微組織由原始等軸β晶粒和球狀初生α相組成,800℃/30min固溶處理后,初生α相變小并逐漸轉變成β相。800℃/30min+500℃/4h時效處理后初生α相全部轉變成β相,且有少量次生球狀α相從β基體中析出;當時效時間增至12h時,α相析出的數量明顯增加,且轉變?yōu)獒槹魻?同時β晶粒得到細化。拉伸試驗結果表明,該合金力學性能中的抗拉強度在經過時效熱處理后明顯高于熱軋態(tài)和固溶態(tài)合金。經過800℃/30min+500℃/12h處理以后,合金的硬度及抗拉強度達到最大值,其延伸率和斷面收縮率并沒有明顯的降低。斷口分析表明,熱軋態(tài)及固溶態(tài)合金的斷口形貌為典型的韌性斷裂;而時效后的合金在塑性變形過程中表現為脆性和韌性相結合的混合型斷裂模式。在外加總應變控制的低周疲勞加載條件下,不同狀態(tài)的該合金在0.4%~0.8%的外加總應變幅下,均表現出穩(wěn)定的循環(huán)應力響應行為;在1.0%的外加總應變幅下,熱軋態(tài)合金則表現為先循環(huán)軟化,后循環(huán)穩(wěn)定,而時效態(tài)合金表現為循環(huán)穩(wěn)定;在1.2%~1.4%的外加總應變幅下,三種狀態(tài)的合金均表現為循環(huán)軟化。時效處理狀態(tài)下,經500℃/12h時效處理的合金表現出了最高的循環(huán)變形抗力與較高的低周疲勞壽命。不同熱處理狀態(tài)下的合金的塑性應變幅、彈性應變幅與載荷反向周次之間均呈線性關系,可分別用Coffin-Manson公式和Basquin公式來描述。不同熱處理狀態(tài)下合金的循環(huán)應力幅值(35)σ/2與塑性應變幅值(35)?p/2之間也均呈線性關系。疲勞斷口觀察表明,在外加總應變控制的低周疲勞加載條件下,不同熱處理狀態(tài)下合金的疲勞裂紋均以穿晶方式萌生于疲勞試樣表面,并以穿晶方式擴展。
[Abstract]:Titanium alloy is a kind of light alloy developed in 1950s. Because of its excellent performance in mechanical property, corrosion resistance and heat resistance, titanium alloy has gradually become an important structural material in engineering application. Among them, metastable 尾-titanium alloys have attracted more and more attention in recent years because of their high strength, toughness and excellent cold working properties. As a kind of structural material, metastable 尾 -titanium alloy is often applied to the key parts of mechanical structure, and fatigue failure is one of its main failure forms. However, the study of metastable 尾 -titanium alloys is mainly focused on the microstructure, basic mechanical properties and so on. The study on the fatigue properties and microstructure changes of Ti-3Al-8V-6Cr-4Mo-4Zr alloys during fatigue deformation is rare. In this paper, (OM), scanning electron microscope (OM),) and (SEM), transmission electron microscope (TEM) were used to study the microstructure of Ti-3Al-8V-6Cr-4Mo-4Zr alloy under different heat treatment conditions. The tensile properties and low cycle fatigue properties were studied systematically. The effect of heat treatment on the microstructure of the alloy was analyzed. The tensile, fatigue deformation behavior and damage mechanism of the alloy under different states were discussed. It is found that the microstructure of hot-rolled Ti-3Al-8V-6Cr-4Mo-4Zr alloy is composed of original equiaxed 尾 grains and spherical primary 偽 phase, and is treated at 800 鈩，

本文編號：2313470