熱處理條件對鈦合金SP-700磨耗特性與腐蝕行為之影響

Effect of heat treatment on wear and corrosion behavior of SP-700 Ti alloy

曾泓文(Hun-weng Tseng)

指導教授 ： 李勝隆

國立中央大學/工學院/機械工程學系/碩士(2015年)

摘要

藉由磨耗與腐蝕實驗，評估不同熱處理對SP-700鈦合金之微結構、抗磨性與耐蝕性之影響。熱處理方式為於850℃固溶後以水淬、空冷、爐冷等不同冷卻速率降至室溫，於500℃再進行1小時時效處理。結果顯示水淬合金之微結構由硬脆初析αp相、α’’相與軟韌βr相所組成，空冷與爐冷合金之微結構皆形成硬脆初析αp相、α相與軟韌βr相，此兩者差別在於空冷合金微結構包含較細緻α相，而爐冷合金則含有較粗大α相。三者硬度為空冷合金最高，其次為爐冷合金，最軟為水淬合金。經時效處理後，由於α’’相與βr析出細小α+β平衡相，合金硬度皆有所提升。
磨耗結果顯示SP-700鈦合金磨耗形式受硬度影響。當材料硬度越高時，其抗磨性越佳。水淬合金由於硬度最低，於磨耗過程中容易產生塑性變形與微裂痕，而導致表面破碎且表面起伏劇烈；硬度稍高的空冷與爐冷合金不易有塑性變形或微裂痕產生，故為線性磨耗溝，表面起伏較小；時效過後的合金，合金硬度皆明顯大幅提升，不易有塑性變形或微裂痕產生，故會形成較淺之線性磨耗溝，且表面起伏最小。
腐蝕研究發現表面α相的多寡與顆粒大小會影響到腐蝕行為的表現，β穩定元素能夠提升抗蝕性，由於α相含有較少β穩定元素，故會增加材料的活性與腐蝕速率。水淬合金會在腐蝕過程中與表層形成鈍化層保護內部，其抗蝕性較佳；空冷與爐冷合金因α相形貌較為粗大且無形成鈍化層保護內部，相對於水淬合金抗蝕性稍差；時效過後，因會析出α相，表面活性與腐蝕速率皆因此增加，故抗蝕性皆差。

關鍵字

SP-700 ； 固溶 ； 時效 ； 磨耗 ； 腐蝕

並列摘要

The effects of different heat treatments on micro-structure, wear and corrosion behavior of SP-700 titanium alloy have been investigated. The process of heat treatments is to cool the temperature by different cooling rate like quench, air-cooling, and furnance-cooling from solution treatment temperature at 850 to room temperature prior to aging. In the process of different cooling rate after solution treatment, the result shows that the structure of the quench cooling alloy forms the hardest αp, hard α'' and soft βr phase. The structure of the air cooling alloy forms the hardest αp and soft βr phase, having the fine morphology. The structure of the furnace-cooling alloy forms the hardest αp and soft βr phase, having the coarse morphology. The alloy strength from high to low is air cooling, furnace cooling, and quench cooling. After aging process, α'' and βr phase transform into stable α+b phase which makes alloy strength increase.
The wear test shows that it attributes the tribology types of SP-700 alloy to titanium alloy strength. The surface of quench alloy having low strength shows the fracture caused by plastic deformation and micro crack during wear test. The surface of aic-cooling and furnance-cooling alloy having higher strength shows sharp and light ditch. After aging, The surface aging alloy shows sharp and light ditch. The wear resist becomes better with increasing strength.
The corrosion test shows that the measure and size of α phase affect the behaviour of the tafel curve bacause α phase lack β-stabilizer element which can improve the protection from corrosion. Quench alloy forms a passive film to protect the interior of alloy. However, air-cooling and furnance-cooling alloy have weaker protection from corrosion owing to the lack of the passive film and the coarse morphology of α phase. After aging, more α phase precipitating causes the weakest protection from corrosion.

並列關鍵字

SP-700 ； solution treatment ； aging ； wear ； corrosion

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