【摘要】：GH4169合金具有良好的高溫力學性能、較強的熱腐蝕抗力以及優(yōu)異的高溫抗氧化性,已廣泛應用于航空航天領域。然而,GH4169合金硬度不高、抗疲勞強度一般,限制了其在航空結構件中的進一步應用。本文通過對GH4169合金進行高能噴丸處理,研究了噴丸時間和彈丸尺寸對合金表面狀態(tài)、表面粗糙度、顯微硬度、殘余應力和表層組織的影響,對比了干噴丸和濕噴丸下合金表層組織和性能差異,探究了GH4169合金噴丸強化機理,獲得了以下結論:GH4169合金干噴丸處理后表面缺陷增多,表面完整性下降。1mm和2mm彈丸噴丸后,試樣表面缺陷主要表現(xiàn)為翹曲,起皮和塌陷。而4mm彈丸噴丸后,試樣表面缺陷主要表現(xiàn)為長條狀和多邊形狀缺陷。干噴丸處理后GH4169合金表面粗糙度、顯微硬度和殘余應力都顯著提升。其中1mm彈丸噴丸3min時,表面粗糙度最小,為2.857μm;4mm彈丸噴丸10min時,表面顯微硬度提升最大,為401HV,較原始試樣硬度(289HV)提升了39%;隨著噴丸時間延長,表層殘余應力場強度增加,1mm彈丸噴丸10min時,表層最大殘余應力達到了-684MPa。XRD分析結果顯示,GH4169合金噴丸后試樣表層無相變發(fā)生,且隨著噴丸時間和彈丸尺寸增加,衍射峰的強度降低,半高寬逐漸增大,表明組織細化程度增加。此外,隨著噴丸時間和彈丸尺寸增大,噴丸作用層厚度不斷增加。4mm彈丸噴丸10min時,噴丸作用層厚度最大,達到450μm。與干噴丸相比,濕噴丸后試樣表面缺陷明顯減少,表面缺陷主要表現(xiàn)為起皮。且隨著彈丸尺寸增大,水對彈丸的緩沖和潤滑作用更顯著,對材料表面完整性的保護程度也越高。濕噴丸后試樣表面粗糙度較干噴丸相比顯著降低,2mm彈丸噴丸10min時,表面粗糙度降低幅度最大,達到了53%。此外,與干噴丸相比,濕噴丸后試樣表面殘余應力更大,2mm彈丸噴丸10min時,表面殘余應力提升了9%左右。GH4169合金經(jīng)噴丸后,表層形成了較強的殘余應力場,表層晶粒內部出現(xiàn)了大量的形變孿晶,且距離噴丸面越近,多系孿晶間的相互交割現(xiàn)象也越明顯,孿晶數(shù)量越多,組織細化程度越高。因此,GH4169合金干噴丸和濕噴丸的表面強化都是由表層組織細化、形變孿晶形成以及殘余應力強化等因素綜合作用的結果。
[Abstract]:GH4169 alloys have been widely used in aerospace industry due to their good mechanical properties at high temperature, strong thermal corrosion resistance and excellent high temperature oxidation resistance. However, the hardness and fatigue strength of GH4169 alloy are not high, which limits its further application in aeronautical structure. The effects of shot peening time and projectile size on the surface state, surface roughness, microhardness, residual stress and surface microstructure of GH4169 alloy were studied in this paper. The microstructure and properties of the alloy under dry and wet shot peening were compared, and the mechanism of shot peening strengthening of GH4169 alloy was investigated. The following conclusions were obtained: the surface defects increased and the surface integrity decreased after shot peening of GH4169 alloy. After shot peening by 1mm and 2mm, the surface defects increased and the surface integrity decreased after shot peening with 1mm and 2mm. The surface defects of the sample mainly show warping, peeling and collapse. However, after 4mm shot peening, the surface defects of the samples were mainly strip and multilateral shape defects. The surface roughness, microhardness and residual stress of GH4169 alloy were improved after shot peening. When 1mm shot peening 3min, the surface roughness was the smallest, and when shot peening 10min was 2.857 渭 m or 4mm, the surface microhardness was the highest, which was 401 HV. the surface roughness was 39% higher than that of the original sample (289HV). With the prolongation of shot peening time, the intensity of surface residual stress field increases. When 1mm shot peening 10min, the maximum residual stress of the surface layer reaches-684MPa.XRD analysis results show that there is no phase change in the surface layer of GH4169 alloy after peening. With the increase of shot peening time and projectile size, the intensity of diffraction peak decreases and the half-maximum width increases, which indicates that the degree of microstructure refinement increases. In addition, with the increase of shot peening time and shot size, the thickness of the action layer of shot peening increases continuously. When 4mm shot peening 10min, the thickness of shot peening layer is the largest, reaching 450 渭 m. Compared with dry shot peening, the surface defects of wet shot peening samples were obviously reduced, and the surface defects were mainly peeled. With the increase of the size of the projectile, the buffering and lubricating effect of water on the projectile is more obvious, and the protection degree of the surface integrity of the material is also higher. After wet shot peening, the surface roughness of the sample was significantly lower than that of dry shot peening. When 2mm shot peening 10min, the surface roughness of the sample decreased to 53%. In addition, compared with dry shot peening, the residual stress on the surface of wet shot peening is greater than that of dry shot peening. When 2mm shot peening 10min, the surface residual stress increases by about 9%. After shot peening, a strong residual stress field is formed on the surface of GH4169 alloy. There are a large number of deformation twins in the surface grain, and the closer to the shot peening surface, the more obvious the intersecting phenomenon between the multi-system twins is, and the more the number of twins is, the higher the degree of microstructure refinement is. Therefore, the surface strengthening of GH4169 alloy by dry shot peening and wet shot peening is the result of the combined effect of surface microstructure refinement, deformation twin formation and residual stress strengthening.
【學位授予單位】：南昌航空大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG668

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