FGH96镍基粉末高温合金的组织和性能

采用等离子旋转电极法制备FGH96合金粉末,研究了用两种不同成形工艺制备的合金的组织和性能,同时对FGH96粉末高温合金的持久断裂行为和裂纹扩展速率进行了分析和研究。     

长期时效对FGH95镍基粉末高温合金γ'相及晶格常数的影响

在不同温度下对FGH95镍基粉末高温合金进行长期时效处理,通过合金显微组织观察和X射线衍射分析,研究了长期时效对FGH95合金γ'相及晶格常数的影响。结果表明,完全热处理FGH95合金经450和550℃长期时效后,合金中细小γ'相略有长大,其粗化行为符合Lifshitz,Slyozov和Wagner（LWS）粗化动力学理论;随着时效时间的延长,FGH95合金中γ'相的晶格常数有所增加,而γ和γ'两相的晶格错配度减小;与时效时间相比,时效温度对FGH95合金中γ'相尺寸及晶格常数的影响更大。     

FGH95合金等温锻造工艺研究

对FGH95合金细晶制备和超塑性等温变形工艺进行了研究。结果表明，双冷速缓冷处理可以有效细化FGH95合金晶粒，改变γ′相的尺寸和分布，并且通过粗化的γ′相对再结晶晶粒的钉扎作用，使FGH95合金细晶组织保持很高的热稳定性；具有细晶组织的GH95合金进行高、低应变速率组合的等温压缩变形时，在低应变速率条件下，可实现超塑性变形。双冷速缓冷处理 超塑性等温锻造工艺具有较强的适应性，可推广至大尺寸粉末高温合金盘件的等温成形，采用该技术研制的等温锻造FGH95合金盘件具有良好的综合力学性能。     

FGH95粉末高温合金蠕变裂纹扩展有限元数值模拟研究

对FGH95粉末高温合金标准CT试样在700℃下的蠕变裂纹扩展过程进行了有限元数值模拟研究.FGH95合金假设为弹性-蠕变体,蠕变变形采用Norton模型描述.蠕变裂纹扩展模拟时考虑了两种裂纹扩展速率,分别为3.25×10-2mm/h(快速裂纹扩展)和6.5×10-4mm/h(慢速裂纹扩展).数值模拟结果表明:FGH95合金在700℃下发生蠕变裂纹扩展时,弹性变形引起的标准CT试样加载线位移Vc在总位移中起主导作用,蠕变变形引起的加载线位移Vc很小,加载线位移率比值(·Vc)/(·V)远小于1,蠕变变形被限制在临近裂纹扩展路径的细长条带状区域内,裂纹尖端没有发生大范围蠕变变形.上述结果说明FGH95合金在700℃下为蠕变脆性材料,应力强度因子K可作为FGH95合金高温疲劳裂纹扩展的有效驱动力参数.     

C和Hf对FGH97粉末冶金高温合金热力学平衡相析出的影响

借助Therrno-Calc热力学计算软件及相应的镍基高温合金数据库,对不同C和Hf含量的粉末冶金高温合金FGH97进行了热力学计算,并结合了相应的显微组织观察.研究表明,C和Hf的改变会影响合金热力学平衡相的析出,其中影响最为显著的是碳化物相,其次为γ'相.本文为今后优化FGH97合金成分,提高合金性能提供了一定的理论依据.     

FGH95合金高低周复合疲劳行为

为了解高周振动应力对FGH95合金低周疲劳过程的影响,对FGH95合金进行高低周复合疲劳和低周疲劳试验。试验结果表明：在低周疲劳过程中叠加的高周振动明显降低了FGH95合金的低周疲劳寿命;且叠加的高周振动应力越大,FGH95合金的低周疲劳寿命降低程度越大。宏观和体视显微镜下分析的试样断口形貌显示：断口呈平坦区和倾斜区两大部分,表面粗糙,有明显的反光小平面。最后,着重用扫描电子显微镜（SEM）分析疲劳裂纹扩展不同阶段的形貌特征,并对不同试验条件下的相同裂纹扩展阶段的裂缝形貌特征进行比较。     

制粉方式对FGH97合金组织和低周疲劳性能的影响

等离子旋转电极粉(P粉)和氩气雾化粉(A粉)经过相同的制备工艺得到两种合金坯料(P合金和A合金)。对两种合金的显微组织和性能进行表征,研究不同制粉方式对FGH97镍基粉末高温合金组织和低周疲劳性能的影响。结果表明:而相较于P合金, A合金的晶粒尺寸更细,γ′相析出更均匀,基本不存在残余枝晶,晶界碳化物呈点状断续分布; A合金的强度略高,塑性显著优于P合金;与此同时,两种低周疲劳裂纹源均以熔渣型夹杂物为主,但A合金的夹杂物尺寸明显更小; A合金低周疲劳裂纹萌生抗力远高于P合金,前者低周疲劳寿命远超过150000周次,远优于后者(70000周次);且A合金的疲劳性能很稳定。     

镍基双合金扩散偶的拉伸性能研究

采用热等静压(HIP)扩散连接工艺,获得了镍基单晶高温合金与粉末高温合金的扩散偶。研究了热等静压和热处理工艺对扩散偶的组织和拉伸性能的影响。结果表明,不同温度热等静压的扩散偶均实现了冶金结合,瞬时拉伸断口位置处于DD402侧,断裂面为{111}滑移面。随着HIP温度升高,DD402母材的γ′相粒子粗化,FGH95粉末合金母材的再结晶晶粒长大;1 166℃HIP扩散偶热处理后,FGH95粉末合金的γ′相由晶界大尺寸γ′相、晶粒内中等尺寸的和细小的γ′相组成。扩散偶试样的650℃抗拉强度受HIP温度影响小,而屈服强度随着HIP温度升高而降低。     

FGH95镍基合金的组织结构与蠕变行为

通过蠕变曲线测定和组织形貌观察,研究了FGH95合金的蠕变特征与变形机制.结果表明:经高温固溶及"盐浴"冷却后,FGH95合金的组织结构由细小γ'相及粒状碳化物弥散分布于γ基体所组成,由于沿晶界不连续析出的粒状(Ti,Nb)C相可提高合金的晶界强度,并抑制晶界滑移,故使其在650℃、1 034MPa条件下有较小的应变速率和较长的蠕变寿命.合金在蠕变期间的变形机制是位错切割γ或γ'相,其中,当(1/2)<110>位错切入γ相,或<110>超位错切入γ'相后,可分解形成(1/6)<112>肖克莱不全位错或(1/3)<112>超肖克莱不全位错+层错的位错组态;蠕变后期,合金的变形特征是晶内发生单取向和双取向滑移,随蠕变进行位错在晶界处塞积,其引起的应力集中致使裂纹在晶界处萌生及扩展是合金的蠕变断裂机制.     

FGH4102粉末高温合金等温热模拟压缩试验及动态再结晶组织研究

本文研究了新型第四代粉末高温合金FGH4102在等温热模拟压缩过程中的组织演变,对γ′相在动态再结晶过程中的作用进行了探讨。结果表明,热等静压态合金在1 060～1 120℃温度范围变形时,热加工性能较好。1 140℃变形后试样容易发生开裂,合金热加工性能较差。合金在γ+γ′两相区变形时均发生了不同程度的动态再结晶,再结晶晶粒尺寸远小于热等静压态的晶粒尺寸。变形过程中,尺寸较大的γ′相起到促进动态再结晶的作用。变形参数对动态再结晶的影响非常显著。低温高应变速率变形时,γ′相促进动态再结晶形核占主导地位,再结晶晶粒比较细小;高温低应变速率变形时,晶粒长大逐渐占据主导地位,再结晶晶粒尺寸较大。     

Effect of Hf and Zr Contents on Stress-rupture and Fatigue Crack Growth Rate Performances in FGH96PM Superalloy

Four experimental FGH96alloys with various contents of Hf and Zr(0and 0.04%,0.3% and 0.04%,0.6% and 0.04%,0.3%and 0.06%,respectively)were produced using PREP(plasma rotating electrode process)+HIP(hot isostatic pressing)route.The unnotched and notched stress-rupture properties and fatigue crack growth rate(FCGR)of all the experimental alloys were investigated to study the effect of Hf and Zr.Relevant fracture morphology and microstructure were observed by scanning electron microscopy and transmission electron microscopy.The results revealed that appropriate content of Hf could lengthen stress-rupture life,eliminate notch sensitivity and slower FCGR.Microstructure analysis showed that the amount ofγ′phase should be increased or decreased by adjusting Hf and Zr contents,and MC carbide and oxide coupled growth should be increased by adding Hf content,which caused oxycarbide to precipitate along grain boundary and strengthen the alloy.It was found that excessive Zr in Hfcontaining FGH96alloy had certain deleterious effects on stress-rupture property because there was strong Zr segregation at prior particle boundary,leaving a long chain of large-size oxides along the boundary.The optimal content of Hf and Zr in FGH96alloy was 0.6%and 0.04%,respectively.     

Microstructure Characterization and Mechanical Properties of FGH 95 Turbine Blade Retainers

FGH 95 is a powder metallurgy (P/M) processed superalloy,which was developed in the 1980s in China.One of the applications of FGH 95 was high pressure turbine blade retainers.The manufacturing processes used to produce FGH 95 blade retainers consisted of atomization by plasma rotating electrode process (PREP),hot isostatic pressing (HIP) at super-solvus temperature and a sub-solvus solution heat treatment.The material had an equiaxed grain structure (ASTM 6.5-7.5).The γ′ precipitates in as-HIP FGH 95 showed a tri-model distribution.Carbides in the alloy were MC type and precipitated at grain boundaries.The prior particle boundaries (PPB) in the material originated mainly from γ′ phase.Statistics of the mechanical properties data from batch production of the FGH 95 blade retainers were investigated.The as-HIP FGH 95 blade retainers showed high strength at room temperature and 650 ℃,excellent creep resistance and outstanding stress rupture strength at 650 ℃.     

Thermomechanical Fatigue Behavior of Powder Metallurgical Nickel Based Superalloy FGH96

The fracture behavior of the thermomechanical fatigue (TMF) of the powder metallurgical nickel based superalloy FGH96 was investigated under in-phase (IP) and out-of-phase (OP) loadings in the temperature range from 550℃ to 720℃ and the mechanical strain amplitude range from 0. 3% to 0. 8%. The results show that the FGH96 TMF fracture character is intergranular for the IP samples and transgranular cleavage-like for the OP samples, at the same strain amplitude, the fatigue life is shorter for the IP than that for the OP samples that is related to crack propagation along grain boundary on the IP samples, the γ' size is larger in the IP than that in the OP sample, which is related to the bulk diffusion processes accelerated by the tensile strain during the high temperature portion of the IP cycle. Dislocation pairs and stacking faults are main microstructures induced by IP TMF, and they are hindered by the grain boundary, which likely resulted in the crack propagation along the grain boundary in the IP samples.     

热变形对FGH96高温合金原始颗粒边界的影响

通过Gleeble-1500热模拟试验机对热等静压成形FGH96高温合金进行热压缩试验,其中温度为1075℃,变形速率为0.001 s-1,变形量为70%。利用场发射扫描电镜、透射电镜和电子能谱研究了合金原始颗粒边界（prior particle boundary,PPB）的组成,讨论了原始颗粒边界在FGH96高温合金再结晶过程中的作用,并分析了合金热变形对原始颗粒边界的影响。结果表明:热等静压成形FGH96高温合金中的原始颗粒边界主要由Ti的碳化物和γˊ相共同组成;原始颗粒边界对合金热变形再结晶形核起促进作用,对晶粒长大起阻碍作用;合金热变形可以改善原始颗粒边界在组织中的分布,从而使晶粒长大过程顺利进行。     

Thermomechanical Fatigue Behavior of Powder Metallurgical Nickel Base Superalloy FGH96

 The fracture behavior in the thermo-mechanical fatigue (TMF) of the Nickel-base Powder Metallurgy Superalloy FGH96 was investigated under in-phase (IP) and out-of –phase (OP) loadings at the temperature range from 550℃ to 720℃ and mechanical strain amplitude range from 0.3% to 0.8％. The results show that the FGH96 TMF fracture character is intergranular on the IP samples and transgranular cleavage on the OP samples, at the same strain amplitude, the fatigue life is shorter for the IP than that for the OP samples that is related to crack propagation along grain boundary on the IP samples, the γ′ size is larger in the IP than that in the OP sample, which is related to the bulk diffusion processes accelerated by the tensile strain during the high temperature portion of the IP cycle. Dislocation pairs and stacking faults are main microstructures induced by IP TMF, and they are hindered by the grain boundary, which likely resulted in the crack propagation along the grain boundary in the IP samples.     

FGH98合金的再结晶行为

利用扫描电镜和透射电镜对热挤压态和退火态FGH98合金的相析出规律及组织特征进行了分析,并对其再结晶机制进行了深入研究.结果表明：热挤压态FGH98合金在空冷过程中已经发生了少量的再结晶现象,随着挤压温度的提高,体系内位错密度下降.退火态FGH98合金中再结晶机制主要与体系内未回溶的一次γ'相有关,在一次γ'相聚集区再结晶主要以依靠亚晶的聚合和亚晶的长大,或两者的混合机制进行形核;随着一次γ'相的减少,合金还可以通过应变诱发晶界迁移、多晶粒交汇区形核、孪晶叠加等多种方式形核.需要指出的是,FGH98合金中未回溶的一次γ'相在退火处理过程中也会通过部分的回复和再结晶发生软化效应.     

变形FGH96合金涡轮盘物理化学相分析

通过采用物理化学相分析方法对镍基变形FGH96高温合金涡轮盘盘心部分厚度方向上不同位置所取的样品进行分析,在不同的电解液和电解条件下进行电解提取出析出相,然后借助X射线衍射仪(XRD)、电感耦合等离子体原子发射光谱仪(ICP-AES)等手段对相及各相的元素含量进行分析,确定了合金的析出相类型、含量和组成结构式,并将其与各位置的高温蠕变性能差异进行比较和分析,得到涡轮盘厚度方向上微观相的信息并推测其对材料性能的影响,进而探讨指导对工艺生产的改进。研究结果表明:变形FGH96合金涡轮盘厚度方向上γ′相粒径和含量、碳化物和硼化物含量变化较大;在变形FGH96合金涡轮盘厚度方向上,各部位的γ′相质量分数都在30%左右。而且各个部位的γ′相含量存在波动,从目前测得的结果来看,质量分数最高和最低的地方相差约5.7%。各个位置处γ′相的含量和粒径,在涡轮盘厚度方向上越靠近中心处γ′相的粒径越大,但相应位置处的高温蠕变性能则呈现相反趋势;此外,在γ′相粒径最大的地方,γ′相的含量也呈现较大值。