快速凝固FGH95合金粉末中的碳化物及其稳定性

对快速凝固FGH95高温合金粉末中的碳化物及其稳定性进行实验研究,分析了粉末颗粒凝固过程中的热学参数和非平衡溶质分配对碳化物形成过程的影响.结果表明合金粉末中亚稳MC'型碳化物形态的几何完整度随粉末颗粒尺寸减小由规则形态向复杂多样化变化,碳化物在热处理时发生分解与合金元素再分配,其形态由复杂形状为主转变为规则形态的稳定MC型碳化物.     

镍基粉末高温合金枝晶间亚稳碳化物

对急冷凝固镍基高温合金松散粉末热等静压成型合金中亚稳碳化物及其相间反应进行了研究。随着热处理温度的升高,粉末中合金元素的分布逐渐均匀化,但枝晶间 MC 能在较高的温度下保持稳定,使 Ti 和 Zr 在该处仍有较高含量。原始粉末中枝晶间主要分布着块状和花状的 MC 型碳化物,在预热处理过程中粉末枝晶间块状碳化物分解,发生M23C6和 M6C 的析出反应,而花状碳化物的成分及形貌则保持相对稳定。成型合金残余枝晶间分布的碳化物主要由块状 M6C 和 MC 及花状 MC 组成,形变再结晶可以促进枝晶间碳化物的溶解。     

镍基粉末高温合金枝晶间亚稳碳化物

对急冷凝固镍基高温合金松散粉末热等静压成型合金中亚稳碳化物及其相间反应进行了研究.随着热处理温度的升高,粉末中合金元素的分布逐渐均匀化,但枝晶间MC能在较高的温度下保持稳定,使Ti和Zr在该处仍有较高含量.原始粉末中枝晶间主要分布着块状和花状的MC型碳化物,在预热处理过程中粉末枝晶间块状碳化物分解,发生M23C6和M6C的析出反应,而花状碳化物的成分及形貌则保持相对稳定.成型合金残余枝晶间分布的碳化物主要由块状M6C和MC及花状MC组成,形变再结晶可以促进枝晶间碳化物的溶解.     

91211合金碳化物转变的试验研究

91211合金是结合我国资源自行设计的一种镍基铸造合金,其特点是无钻高钨,在高温下具有高强度,合金相的研究表明,合金铸态时存在MC、M_θC两种类型的碳化物,其总量为1.5％。本文应用热处理,电解萃取、化学分离方法,研究碳化物的稳定性及转变的数量关系。     

GH4710合金的相析出特征及其与热加工塑性损伤的关联性

利用Thermal Calc热力学软件、光学金相显微镜、扫描电镜等手段分析了GH4710合金原始态和不同条件热物理模拟变形后的析出相及加工损伤特征,系统研究了析出相特征与该合金热加工塑性损伤及开裂的关联性.结果表明:GH4710合金的原始组织主要由γ’、MC及M₂₃C₆碳化物、γ+γ共晶组织组成;热加工时微孑洞等损伤在MC碳化物及γ+γ共晶组织处形核后沿晶界扩展,最终相互连接导致合金大面积破坏;γ’相优先在MC碳化物及共晶组织附近析出,并通过其共格应力场的作用增加了损伤形核和扩展阻力,使合金在较低温度下的塑性损伤值明显小于高温条件下.     

含Hf和Ta新型镍基高温合金粉末中碳化物相

对含Hf和Ta新型镍基高温合金FGH98Ⅰ等离子旋转电极(PREP)雾化原始和不同温度下预热处理粉末中的碳化物相进行了研究.结果表明:原始粉末中MC′型碳化物可分为两类,一类为富Ti、Ta和Nb,另一类为含Ta、Hf和Zr.两类碳化物均含有一定量非碳化物形成元素Co和Ni及中等强碳化物形成元素Cr和Mo,并以块状、粒状分布于枝晶或胞晶间;随着预热处理温度升高,粉末中富Ti、Ta和Nb的MC′型碳化物转变为MC型碳化物,且其所含Ti、Ta和Nb的总量增大;含Ta、Hf和Zr的MC′型碳化物发生分解和转变,析出稳定的M23C6、M6C和MC型碳化物,M23C6碳化物的析出和溶解温度为950℃和1150℃,M23C6和M6C碳化物共存温度为1000～1100℃.另外,粉末中微量元素Hf和Ta主要以碳化物和γ′相参与碳化物反应.     

长期时效对燃气轮机叶片用镍基高温合金微观组织的影响

研究了燃气轮机叶片用镍基高温合金在800℃、850℃和900℃下分别长期时效1000h、3000h和5000h后的组织.结果表明,γ’沉淀相生长动力学遵循LSW熟化理论,长期时效过程中一次碳化物MC主要退化为M23C6型碳化物,且未发现有害相TCP相,表明合金具有良好的热稳定性.     

K465合金的显微组织和性能研究

研究了铸态、热处理态及含0.02%(质量分数)Mg的K465镍基铸造高温合金的显微组织、力学性能.研究结果表明:铸态K465合金组织主要由γ基体、弥散分布的γ′相、(γ+γ′)共晶和碳化物组成,室温平均抗拉强度960MPa,伸长率6.0%,975℃/230MPa条件下平均持久寿命28.1h;经1210℃/4h+空冷的固溶热处理后,晶界MC碳化物部分转变为M6C碳化物,γ′相颗粒尺寸减小到0.1～0.2μm,合金室温平均抗拉强度1055MPa,伸长率4.0%,975℃/230MPa条件下平均持久寿命为50.3h;加入0.02%(质量分数)Mg后,合金中MC碳化物球化,室温平均抗拉强度990MPa...     

GH586合金的晶界碳化物高温强化

通过对ＧＨ５８６合金在不同固溶处理温度下的金相组织观察,晶界碳化物萃取复型的透射电镜观察,定量相分析及８５０℃拉伸性能的测试,研究了晶界碳化物对合金高温拉伸性能的影响,探讨了高温下合金晶界碳化物的强化作用,并结合理论分析提出了晶界碳化物高温强化关系式。结果表明,该合金中均匀分布的细小晶界碳化物在高温下提高了合金强度;晶界碳化物对８５０℃屈服强度的贡献,用理论模型分析的结果与实验结果符合良好。     

GH586合金的晶界碳化物高温强换

通过对GH586合金在不同固溶处理温度下的金相组织观察、晶界碳化物萃取复型的透射电镜观察、定量相分析及850℃拉伸性能的测试,研究了晶界碳化物对合金高温拉伸性能的影响.探讨了高温下合金晶界碳化物的强化作用,并结合理论分析提出了晶界碳化物高温强化关系式.结果表明,该合金中均匀分布的细小晶界碳化物在高温下提高了合金强度;晶界碳化物对850℃屈服强度的贡献,用理论模型分析的结果与实验结果符合良好.     

Microstructure and stress rupture properties of polycrystal and directionally solidified castings of nickel-based superalloys

A new directionally solidified Ni-based superalloy DZ24, which is a modification of K24 alloy without rare and expensive elemental additions, such as Ta and Hf, was studied in this paper. The microstructure and stress rupture properties of conventionally cast and directionally solidified superalloys were comparatively analyzed. It is indicated that the microstructure of K24 alloy is composed of γ, γ′, γ/γ′ eutectics and MC carbides. Compared with the microstructure of K24 polycrystalline alloy, γ/γ′ eutectic completely dissolves into the γ matrix, the fine and regular γ′ phase reprecipitates, and MC carbides decompose to M₆C/M₂₃C₆ carbides after heat treatment in DZ24 alloy. The rupture life of DZ24 alloy is two times longer than that of K24 alloy. The more homogeneous the size of γ′ precipitate, the longer the rupture life. The coarsening and rafting behaviors of γ′ precipitates are observed in DZ24 alloy after the stress-rupture test.     

Pore defects in a nickel-based superalloy with high Ti content

Pores are uncommon defects in superalloy bars, which deserve to be investigated. In this work, a type of pore defect within GH4710 nickel-based superalloy was investigated by 3D X-ray imaging method combined with metallographic analysis. 3D X-ray imaging was used for locating and visualizing the defects in the alloy. The 3D X-ray imaging result of the defects showed a good agreement with the defect anatomical morphologies. It was observed that the pore defect was accompanied by MC carbides, micro-crack, and non-metallic inclusions. The origin of pore defect was attributed to the shrinkage pores, inclusion and the complex precipitates. The analysis showed that the pore defects in GH4710 alloy was associated with strong micro-segregation and complex phase precipitation during solidification, induced by the high weight content of Ti and C in the alloy.     

过滤净化对K640S返回料力学性能的影响

对铸造钴基高温合金K640S返回合金进行过滤净化处理,测试合金化学成分、拉伸性能和蠕变性能·结果表明:过滤明显降低合金中的O、N元素的质量分数,而其他主要元素质量分数没有变化·过滤对合金拉伸性能没有明显影响·在815℃、205MPa条件下,过滤合金与未过滤合金相比,蠕变寿命从34h提高到64h·过滤后合金组织中显微疏松明显减少·可见,返回合金经过滤处理后,其性能已达到新料的性能水平·     

钒含量对高碳高钒高速钢组织与性能的影响

对高碳高钒高速钢的显微组织、硬度及热处理工艺进行了试验研究 ,结果表明 ,其显微组织中存在有MC、M6C和M2 C型三种类型的合金碳化物 ,其中MC型碳化物起主要作用。随着含钒量的增加 ,钢中MC型碳化物数量增加 ,其形态由不连续网状向颗粒状转变。     

GH220合金中晶界针状碳化物的成因

研究了镍基高温合金在1123K,392MPa下周期持久断裂过程中晶界针状碳化物的析出过程。分析了它的形成原因,实验采用二种热处理工艺,得到二种不同的晶界状态:直晶和弯晶。透射电镜分析结果表明,无论何种晶界状态,晶界碳化物都有一个由颗粒状碳化物向针状碳化物转化的过程。而弯晶处理的合金,首先发生由弯晶向平直晶界的转变,即尺寸较大且不规则状的晶界碳化物逐渐断裂成颗粒状排列的晶界碳化物,该过程所需时间较长,这就解释了弯晶合金比如直晶合金针状碳化物量少的原因。提出了一个由颗粒状碳化物向针状碳化物转化的模型。     

喷射成形含铌 M3型高速钢的组织和耐磨性

采用喷射成形技术制备了 M3型高速钢和以 Nb 替代 V 的 M3型高速钢。利用扫描电镜、X 射线衍射、差示扫描量热仪和金相显微镜研究了 Nb 对 M3型高速钢组织的影响。喷射成形能有效消除宏观偏析,细化组织。以 Nb 代 V,提高了 MC 型碳化物开始析出温度,大量 MC 相先于共晶反应析出,呈独立的近球形分布于晶界,同时其尺寸减小。由于消耗大量 C,抑制了共晶反应,M2 C 片层数量减少且厚度变薄,其在热变形过程中更易于分解,进一步增加了组织均匀性。低温低载荷时含铌的 M3型高速钢抗磨损性能显著优于 M3高速钢,温度升高到500℃时磨损机制逐渐以氧化磨损为主,两合金的抗磨损性能差距减小,主要原因是大量呈弥散球形分布的含铌 MC 型碳化物能有效提高高速钢的磨粒磨损抗性,而其对抗氧化性能并无明显作用。     

Effect of oxygen content and heat treatment on carbide precipitation behavior in PM Ni-base superalloys

The influence of oxygen content and heat treatment on the evolution of carbides in a powder metallurgy (PM) Ni-base superalloy was characterized. The results reveal that oxygen content has little influence on the precipitation of carbides inside the particles. However, under the consolidated state, stable Ti oxides on the particle surface act as nuclei for the precipitation of prior particle boundaries (PPB). Also, oxygen can diffuse internally along grain boundaries under compressive stress, which favors the precipitation of carbides inside the particles. Therefore, a higher amount of carbides will appear with more oxygen content in the case of consolidated alloys. It is also observed that PPB can be disrupted into discontinuous particles at 1200℃, but this carbide network is hard to be eliminated completely. The combined MC-M₂₃C₆ morphology approves the nucleation and growth mechanism of carbide evolution.     

电渣重熔过程冷却强度对含镁H13钢中碳化物的影响

研究电渣重熔过程冷却强度对含镁H13钢凝固组织和碳化物偏析的影响.采用光学显微镜、扫描电镜、透射电镜、X射线衍射仪等分析凝固组织及碳化物的特征.研究发现,钢锭的凝固组织均为马氏体组织、残余奥氏体及一次碳化物.H13钢电渣锭中主要析出的一次碳化物为V8C7、MC、M23 C6及M6C.随着冷却强度增加,电渣锭边部碳化物的尺寸减小且分布更加均匀,但是碳化物的类型不发生变化.电渣重熔过程中冷却强度增加促进钢中镁对夹杂物的变性能力,经过镁变性后生成的MgO· Al2O3为TiN的析出提供形核质点,MgO· Al2 O3和TiN的复合夹杂物能够促进一次碳化物异质形核,从而细化一次碳化物.     

Microstructural evolution of a heat-treated H23 tool steel

The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures (1100℃ and 1250℃), followed by water quenching and double-aging at 650℃, 750℃, and 800℃ with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched microstructures, which consisted of a ferrite matrix, M₆C, M₇C₃, and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M₆C, M₇C₃, and M₂₃C₆ carbides. Secondary hardening as a consequence of secondary precipitation of fine M₂C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250℃ and double-aging at 650℃, which suggested that this tool steel should be used at temperatures below 650℃.     

Low cycle fatigue behavior of micro-grain casting K4169 superalloy at room temperature

The strain-controlled low cycle fatigue tests were carried out at 298 ?K for the newly developed micro-grain casting K4169 superalloy, and the cyclic stress response, deformation and fracture behaviors of the alloy were studied. The results show that the fatigue life of the alloy was increased by more than two times compared with other casting K4169 alloys. This can be partly attributed to grain refinement impeding crack initiation and propagation. When the strain amplitude was in plastic range (Δε_t/2 ?≥ ?0.5%), the alloy displayed a short period of initial cyclic stability followed by cyclic softening to fracture. By observing dislocation configurations, only a few dislocations moved around grain boundaries at initial cycles, leading to short cyclic stability. Afterwards, dislocations in the slip bands cut γ" phase continuously leading to cyclic softening. When the strain amplitude was in elastic range (Δε_t/2 ?≤ ?0.4%), the alloy exhibited elastic deformation and the peak stress kept stable. In addition, the crack initiation site changed from the MC carbides to the persistent slip bands on surface with increasing strain amplitudes.