本文選題：GH625合金 + 析出相�。� 參考：《蘭州理工大學》2017年碩士論文

【摘要】：為加強國產(chǎn)高溫合金在民用領(lǐng)域內(nèi)的高端應(yīng)用,并從現(xiàn)階段我國電力系統(tǒng)急需大力發(fā)展超超臨界火電技術(shù),以滿足經(jīng)濟發(fā)展對低污染能源需求的實際出發(fā),本文選擇700℃超超臨界機組耐熱部件的候選材料GH625合金為研究對象,采用掃描電子、能譜、X-ray衍射和透射電子等分析手段,并通過常溫拉伸和硬度測試試驗,考察了某一國產(chǎn)GH625合金在720℃下經(jīng)長時時效后其組織與力學性能的變化,旨在為國產(chǎn)GH625合金的實際應(yīng)用提供參考。實驗得出的結(jié)果如下:(1)通過研究合金在720℃下,經(jīng)1×103 h、3×103 h和5×103 h時效后,其析出相與組織的演變過程。從中發(fā)現(xiàn),碳化物的分解與轉(zhuǎn)變、γ"相的相接和δ相的析出與長大,是影響晶界形貌變化的主要因素,隨時效時間的延長晶界形貌呈現(xiàn)出先粗化后細化再粗化的變化過程;晶內(nèi)主要沉淀相依照γ'、γ"和δ相的次序先后析出,且隨時效時間的延長晶內(nèi)存在γ"相向δ相的轉(zhuǎn)變,γ"相的過分粗化是該轉(zhuǎn)變發(fā)生的主要因素。時效1×103h的晶內(nèi)沉淀相以均勻分布的γ'、γ"相為主,時效3×103h的晶內(nèi)沉淀相分布不均勻,γ'、γ"和δ相均出現(xiàn)在基體中,時效5×103h后,晶內(nèi)沉淀相則以δ相為主。(2)利用X-ray衍射分析,測定試樣經(jīng)不同時效時間后熱暴露面氧化層的物相結(jié)構(gòu)。結(jié)果表明,NiO、Cr_2O_3和NiCr_2O_4是形成表面氧化層的三種主要物相。(3)基于Ostwald熟化理論,分析γ"相的熱穩(wěn)定性和粗化過程。結(jié)果表明,γ"相的粗化符合Ostwald熟化理論,在時效4.541×103h后γ"相在粗化速度較快方向上的尺寸開始趨于一致,其最大平均尺寸為0.24253μm,且在時效過程中γ"相的形貌尺寸分布與該理論中似穩(wěn)態(tài)分布函數(shù)的描述高度吻合。同時發(fā)現(xiàn)γ"相的相變動力學曲線滿足Avrami方程,并求得阿弗拉密指數(shù)n約為1符合試驗中的實際情況。(4)通過對合金力學性能的測試結(jié)合斷口形貌觀察,分析合金組織與性能的聯(lián)系,并以修正后的Hollomon模型,求得加工硬化曲線與硬化指數(shù)。結(jié)果表明,合金中主要強化相的含量與其力學性能相關(guān)聯(lián);利用加工硬化曲線可求得,硬化在交滑移控制開始時的位錯密度值為2.55858×1011cm-2,而該模型下的硬化指數(shù)則與應(yīng)變相關(guān)。(5)將國產(chǎn)GH625合金與國際鎳公司在相同成型方式和熱處理工藝條件下,生產(chǎn)的Inconel 625合金的力學性能進行對比。結(jié)果表明,國產(chǎn)GH625合金在主要的室溫力學性能指標上差別不明顯,但在700℃左右的條件下經(jīng)長時時效后,在拉伸強度和塑性方面均不及Inconel 625合金。從強化相的析出過程來看主要原因是,國產(chǎn)GH625合金的主要強化γ"相的粗化較快,熱穩(wěn)定性不如Inconel 625合金,導致在本次時效試驗的后期大量的δ相過早析出,基體中的固溶元素含量不斷減少,弱化了固溶強化的效果所致。(6)對比歐洲700℃超超臨界機組(耐熱部件)的選材標準。結(jié)果表明,該批次合金在720℃下,在105h時效后其氧化失重粗略估算為4.45×10-3g/mm2,滿足選材的適用性要求,但在高溫環(huán)境下合金長期服役過程中組織的穩(wěn)定性還需提高。
[Abstract]:In order to strengthen the high-end application of domestic high temperature alloy in the civil field, and from the current stage, our power system needs to develop ultra supercritical thermal power technology urgently in order to meet the demand of low pollution energy for economic development. This paper selects GH625 alloy as a candidate material for the heat-resistant components of a super supercritical unit at 700 C as the research object. The changes in the microstructure and mechanical properties of a homemade GH625 alloy at 720 C at 720 C were investigated by drawing electron, energy spectrum, diffraction and transmission electron. The changes of microstructure and mechanical properties of a homemade GH625 alloy at 720 C were investigated in order to provide reference for the practical application of domestic alloy. The results are as follows: (1) through research After aging at 720 C, the evolution process of the precipitated phase and tissue after 1 x 103 h, 3 x 103 h and 5 x 103 h is found. It is found that the decomposition and transformation of carbides, the precipitation and growth of the phase and delta phase are the main factors affecting the change of grain boundary morphology, and the grain boundary morphology shows the first coarse-grained and then coarsening changes with the aging time. The main precipitates in the crystal are precipitated in the order of gamma ", gamma" and delta phase in the crystal, and with the time prolonging of the crystal memory in the gamma "phase to delta phase, the overcoarsening of the phase of gamma" is the main factor of this transformation. The internal precipitation phase of the aged 1 * 103h is dominated by the uniform distribution of gamma and gamma phase, and the distribution of the precipitate phase in the aging 3 * 103h is not distributed. Homogeneous, gamma, gamma and delta phase appear in the matrix. After aging 5 * 103h, the precipitates in the crystal are mainly delta phase. (2) X-ray diffraction analysis is used to determine the phase structure of the surface oxidation layer of the heat storm after different aging time. The results show that NiO, Cr_2O_3 and NiCr_2O_4 are the three main phases of the formation of the surface oxidation layer. (3) based on the Ostwald ripening. The theory is to analyze the thermal stability and coarsening process of the gamma phase. The results show that the roughening of the gamma phase conforms to the Ostwald ripening theory. The size of the phase in the fast direction of the roughening rate begins to conform to the size of 0.24253 m after the aging of 4.541 * 103h, and the size distribution of the gamma phase in the aging process is similar to that in the theory. The description of the distribution function is highly consistent. At the same time, it is found that the phase transformation kinetics curve of the phase satisfies the Avrami equation and the AMF n index is about 1 in accordance with the actual conditions in the experiment. (4) the relationship between the microstructure and properties of the alloy is analyzed by the test of the mechanical properties of the alloy and the fracture morphology, and the modified Hollomon model is obtained. The results show that the main hardening phase content in the alloy is related to the mechanical properties of the alloy, and the dislocation density value at the start of the cross slip control is 2.55858 * 1011cm-2 by the processing hardening curve, and the hardening exponent under this model is related to the strain. (5) the domestic GH625 alloy and the international The mechanical properties of Inconel 625 alloy produced in the same molding and heat treatment conditions were compared. The results showed that the difference in the main mechanical properties of GH625 alloy was not obvious, but under the condition of long time aging at about 700 C, the tensile strength and plasticity of the alloy were less than that of Inconel 625. From the precipitation process of the enhanced phase, the main reason is that the main intensification of the GH625 alloy in China is that the coarsening of the phase is faster and the thermal stability is not as good as the Inconel 625 alloy, which leads to the early precipitation of a large number of delta phase in the later period of this time test, the content of solid solution elements in the matrix is less and less, and the effect of solid solution strengthening is weakened. (6) contrast Europe. The material selection standard of the 700 C super supercritical unit (heat-resistant unit) at 700 C shows that the weight of the batch alloy at 720 C is roughly estimated at 4.45 x 10-3g/mm2 after aging, which meets the application requirements of the material, but the stability of the fabric in the long service process of the alloy needs to be improved in the high temperature environment.

【學位授予單位】：蘭州理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG132.3

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