The effect of heat treatment on the microstructure and mechanical properties of a high-boron Ni3Al-based superalloy was investigated by scanning electron microscope, tensile test and stress rupture test. The results show that when the solid solution temperature increases from 1080 degrees C to 1150 degrees C, the volume fraction of gamma ' phase in dendrite trunk decreases gradually, the morphology changes from blocky to spherical, and fine tertiary gamma ' phases are precipitated inside the gamma channel. When the temperature rises from 1080 degrees C to 1120 degrees C, the skeleton-like primary borides are partially dissolved, and the granular secondary borides are precipitated. The precipitation tendency of secondary borides is increased with the increase in temperature, and the borides are completely dissolved when the temperature rises to 1150 degrees C. After aging at 900 degrees C for 10 h, the alloy solid-solution-treated at 1080 degrees C achieves the ultimate tensile strength of 900 MPa during the tensile test at 800 degrees C and the stress rupture life of 144.5 h under the condition of 580 MPa/800 degrees C, exhibiting the best comprehensive mechanical properties. Therefore, the optimal heat treatment process of the test alloy is 1080 degrees C & times;4 h -> air cooling+900 degrees C & times;10 h -> air cooling.

This study aimed to optimize the grain structure of complex thin-walled nickel-based superalloy castings by investigating the influence of key casting parameters using both cellular automaton–finite element (CAFE) simulations and experimental validation. The main problem addressed was the inhomogeneous grain morphology arising from complex mold geometries and uneven thermal conditions during investment casting. The solidification process was simulated using the ProCAST software, incorporating the CAFE method to model temperature fields and grain growth dynamics. The results revealed that the molten metal flow pattern during mold filling significantly affected the local temperature field and subsequent grain formation. Specifically, simultaneous bidirectional filling minimized thermal gradients and suppressed coarse columnar grain formation, promoting finer, more uniform equiaxed grains. Lowering the pouring temperature (to 1430 °C) in combination with reduced shell temperature (600–800 °C) enhanced nucleation and improved grain uniformity in thin-walled regions. Higher cooling rates also refined the grain structure by increasing undercooling and limiting grain growth. Experimental castings confirmed these simulation outcomes, demonstrating that the proposed optimization strategies can significantly improve grain homogeneity in critical structural areas. These findings provide a practical approach for controlling microstructure in large, intricate superalloy components through targeted process parameter tuning.

Cold deformation behavior and microscopic mechanisms of L605 centrifugal cast tubes were studied via room-temperature compression tests. The hardening behavior aligned well with the Hollomon equation, and a high-fidelity cold deformation constitutive relationship was determined using least-squares fitting in Matlab. Increasing cold deformation intensified grain distortion, promoted grain uniformity, and transformed the original columnar grains into elongated strip shapes. During deformation, twin boundaries with an orientation deviation of 60° remained at 1–4 %, whereas low-angle grain boundaries rose markedly, and high-angle grain boundaries declined. At 15 % compression, numerous dislocations were observed within stacking faults, along with SMIT processes. Upon further compression to 30 %, abundant stacking fault intersections emerged, and a geometric model yielded a dislocation motion resistance of 0.784 N m −1 . Subsequent annealing of compressed specimens at 1,100 °C for 30 min unveiled abundant Σ3 (60°⟨111⟩) annealing twin boundaries, demonstrating an inverse relationship between deformation level and annealed grain size. Microscopic M 6 C carbides were trapped at interfaces between annealing twin boundaries and grain boundaries. Additionally, stacking faults arranged in orderly, parallel arrays on annealing twin surfaces, hindering the γ -to-ε phase transition.

The high-temperature oxidation behavior of novel Co-Cr-Nb-W carbide-strengthened wear-resistance alloys with different Al contents (1wt

A novel Co-Cr-Nb-W alloy with a carbide-dominant microstructure was designed in view of the excellent characteristics of NbC and gamma-Co matrix to use as wear-resistant components on integral shrouds. The actual service conditions of the alloy were simulated using heat treatment experiments to investigate the influence of high temperature on their microstructure and mechanical properties. The stress-rupture property of the alloy was improved by exposing them to high temperatures. Carbides in the matrix bore the main load under external stress. The fracture mechanism of the Co-Cr-Nb-W alloy is ductile combined with localized brittle failure around large carbides. M 6 C was formed from the degeneration of MC and decomposition of M 23 C 6 during the heat treatment process along with the two carbides transformation as follows: MC + matrix -* M 6 C and M 23 C 6 + matrix -* M 6 C. The elimination of lamellar M 23 C 6 by carbide transformation and supplemental precipitation of fine M 6 C around skeleton MC were conducive to longer rupture life. Stacking faults (SFs) played a crucial role in the strengthening mechanism of the Co-Cr-Nb-W alloy. The external stress activated different slip planes in the gamma matrix to form "X-shaped" crossing stacking faults (CSFs). Lomer-Cottrell (L-C) locks in CSFs were confirmed by transmission electron microscopy (TEM) under two-beam conditions. SFs can interact with precipitates, dislocations, and grain boundaries to enhance the strengthening mechanism. The SF width was increased by heat treatment, which further increased the dislocation accumulation in the matrix and promoted the formation of CSFs and L-C locks. Therefore, the heat treatments were beneficial to the enhancement of the stress-rupture property of the Co-Cr-Nb-W alloy.

Carbides transformation during heat-treatment process has a significant effect on the mechanical properties of superalloys. The distribution and evolution mechanism of carbides and their effects on high-temperature tensile properties of Co-Cr- Nb-W wear- resistant alloy during heat treatment process were investigated by XRD, SEM, EPMA, and TEM. There are two carbides transformation processes in the Co-Cr- Nb-W alloy during brazing simulation and aging: MC+ matrix=M6C and M23C6+matrix=M6C. The fracture mechanism of the Co-Cr-Nb-W alloy under high temperature tensile stress is a hybrid mechanism of ductile fracture and brittle fracture, and the interface between the bulk primary carbide and the matrix is easy to become the source of crack source. The heat treatment process eliminates the lamellar M23C6, which is easy to cause grain boundary migration, induces the precipitation of fine M6C particles around the skeleton MC, improves the interdendritic element segregation, promotes the formation of high- density overlapping stacking fault bands in the matrix, and increases the tensile strength of the alloy at 1000 degrees C by about 20 MPa.

为研究L605离心铸管在凝固过程中不同温度梯度下组织的生长规律,利用ProCAST软件对管坯内部不同区域的组织进行了数值模拟,并在铸型前端设置感应加热线圈实现在线加热,以消除充型过程中铸型自前端至后端随着金属液充型的进行所增加的温度梯度.结果发现,模拟结果与试制结果吻合较好,可以反映管坯凝固组织中柱状晶和等轴晶的形貌与面积比,为预测其凝固组织生长过程提供了有效依据,得到了适合该离心铸管的较优的铸型温度为500℃.

采用真空连铸+离心铸造工艺制备了φ50 mm的L605离心铸管,分析了 L605管坯中的气体、有害元素的含量和非金属夹杂物.结果表明,真空连铸/离心铸造工艺是提高铸管纯净度的有效方法,试制L605合金中O含量为0.000 4％,N含量为0.006％,S含量为0.000 9％,P含量＜0.001％.L605管坯非金属夹杂物含量低于0.2 mg/kg,95％以上的夹杂物尺寸小于2.5μm,纯净度很高,满足了 L605细径薄壁管的加工要求.

The applied force of fluid particles in the filling process of horizontal centrifugal casting was analyzed, and the precipitation separation time of different kinds of inclusions and optimal pouring temperature were deduced according to the movement law of inclusions. The movement trajectory of inclusions in the filling process of horizontal centrifugal casting was established using ProCAST software, and the numerical simulation and process optimization of the movement trajectory and final residence position of inclusions in centrifugal casting pipes under different rotating speeds were carried out. The results show that the smaller the density of inclusions is and the larger the particle size is, the shorter the separation time is. It is found that 5 mu m SiO2 inclusions are most likely to be thrown out of the liquid metal under the action of centrifugal force and finally stay on the inner surface of the cast pipe. The optimal pouring temperature for L605 centrifugal casting pipe is 1580 degrees C, and the optimal centrifugal speed is 2800 r/min. Under the condition of these optimal process parameters, the actual casting experiment of centrifugal cast pipe was carried out, and the inclusion distribution information was obtained by optical microscope (OM) and scanning electron microscope (SEM-EDS). The microscopic analysis result of inclusions in actual castings is consistent with the simulation result, which verifies the effectiveness of the prediction and simulation results.

针对我国新一代航空发动机叶冠表面强化用高温耐磨材料的迫切需求,采用熔炼铸造法制备出一种以碳化铬和NiAl相作为耐磨硬质相的新型Ni3Al基高温耐磨合金.显微组织分析、室温硬度测试、高温抗氧化性测试结果显示,两种耐磨硬质相大量析出并且均匀分布于合金中.与现役的高温耐磨材料相比,该合金同时具备高的室温硬度和1050℃时优异的抗氧化性,有望成为新一代高温耐磨材料.

The oxidation behavior of NbC particle-reinforced cobalt-based wear-resistant alloy in the air from 950 to 1050 degrees C was investigated. The alloy belongs to the oxidation-resistant level below 950 degrees C, the sub-oxidation-resistant level below 1000 degrees C, and the non- oxidation- resistant level below 1050 degrees C. The oxidation kinetic curves basically comply with the parabolic law. A mixed oxide layer consisting of CoCr2O4, CoNb2O6, Cr2O3, and Al2O3 is established on the alloy surface. The preferential in-situ oxidation behavior of the blocky NbC phase in the matrix results in the loose porous oxide layer and a non- uniform thickness. After oxidation at 1050 degrees C for 100 h, a Cr-depletion zone is formed in the matrix below the oxide layer, leading to the inability to re-form a continuous and protective oxide film after oxide peeling.

The effects of Hf addition on the microstructure, solidification behavior and porosity of a nickel-based high-boron cast superalloy were studied. The results of microstructure analysis, differential thermal analysis (DSC) and isothermal solidification quenching test show that Hf segregates in interdendritic regions during the solidification process of the alloy, and precipitates from the residual liquid phase in the form of Ni5Hf phase at the end of the solidification process. The addition of Hf reduces the precipitation temperature of liquid/solidus, gamma/gamma' eutectic phase and boride, delays the solidification process of the alloy, widens the solidification temperature range from 166.3 degrees C to 200.5 degrees C, and significantly increases the content of gamma/gamma' eutectic phases. A thin-walled tube cast is independently designed by the authors. Penetration test results show that the addition of Hf remarkably reduces the porosity of the thin-walled tube, and the tendency of porosity forming of the alloy is obviously reduced.

This paper investigates the evolution behaviors of inclusions in the warm rolling process of L605 thin‐walled tubes and analyzes their influencing mechanism. Homogeneous spherical and irregular SiO 2 –Al 2 O 3 –Cr 2 O 3 (MnO + CaO) inclusions are observed in the cast tubes. After warm rolling, the homogeneous inclusions are changed into heterogeneous spherical ones with gray‐colored (Al 2 O 3 )‐rich phase and dark‐colored (SiO 2 )‐rich phase and Cr 2 O 3 (MnO + CaO)‐rich phase due to different deformability of various inclusions under the combined effects of diameter reduction and wall pressure. As the rolling times of tubes increases, large‐sized inclusions are crushed continuously, and the average size of the inclusions gradually decreases. At the same time, the number density of inclusions presents a first increasing and then decreasing trend. It is estimated that the critical size of the inclusions that are hard to further crack in warm rolling is about 0.5 μm. Meanwhile, the inclusions would lead to stress concentration at the positions near large‐sized irregular inclusions, causing cracks and penetrating defects. The simulation results show that the stress near the outer diameter of the inclusions is twice that in the middle and the changes of stress in the 30 μm inclusions and nearby areas exhibit a significant increase compared to the small‐sized 2 μm inclusions.

分析了不同类别JG4246A返回料清洗处理前后表面夹杂物种类及分布.结果发现,返回料清洗前表面以与型壳反应后生成的Al2O3夹杂物为主,面积分数为24％～25％,同时存在少量HfO2、富Ti氧化物及富Zr和Hf的氧化物.返回料处理后,表面仍存在一定数量Al2O3夹杂物,少量富Hf、富Zr和Si夹杂.返回料100％清洗并熔化后浮渣较多,无法满足返回料再利用需求,需进一步提高返回料母合金洁净度.

采用ProCAST软件对K4169合金的离心铸造工艺进行了模拟研究.通过分析浇注速度、铸型转速、浇注温度及铸型温度对离心铸管充型及凝固行为的影响,获得了外径56 mm/内径38 mm的K4169合金离心铸管最佳制备工艺参数.在此工艺参数条件下,K4169合金离心铸管可实现连续稳定充型,离心铸管壁厚差为0.2 mm,内表面疏松比例小于3％,且柱状晶平均宽度为1.7 mm.结合模拟结果对K4169合金离心铸管进行试制,所制备的离心铸管显微组织中柱状晶占比80％,且晶粒组织细小,因而离心铸管具有优异的高温塑性.

The 100％ DZ125 revert superalloy was purified into revert ingot by vacuum horizontal continuous casting(VHCC).The inclusion level of revert ingot was determined by electrolysis.The chemical composition analysis,gas content and microstructure were also investigated.The results show that the content of bulky inclusions in vacuum casting DZ125 alloy ingot reaches the level of virgin alloy,which is reduced to 5.74 mg/(10 kg) from average 8.30 mg/(10 kg).The chemical composition,oxygen and nitrogen content,and microstructure of the revert alloy exhibit little difference with the virgin alloy,which can fully meet the requirement of DZ125 alloy technical standard.

The inclusions types and distribution in DZ125 superalloy revert were analyzed by SEM,EDS.The results show that the inclusions in the revert surface are mainly mixed oxides,such as HfO2,Al2O3,SiO2,etc,and the carbon,nitrogen and sulphur mixed inclusions grew up with the abnormal growth of MC.The internal inclusions of the reverts are mainly Mg-Al-Si-Hf mixed oxides and purity HfO2,etc.Combining with the alloy melting process and the Gibbs free energy of the different kinds of inclusions,the forming mechanism of the revert surface and internal inclusion was explained.The surface inclusions is generated by the oxide reaction of the alloy and the auxiliary materials--SiO2.The internal inclusion is mainly generated by three ways of auxiliary material drop,oxidation endogenous and raw material left.

K418 superalloy barstock were manufactured by vacuum horizontal continuous casting (VHCC)technology.The inclusion,microstructure and corresponding mechanical properties of VHCC K418 superalloy were analyzed.The results show that the inclusions of VHCC K418 superalloy drop sharply 80%,the microstructure is fine and the fatigue life in-crease significantly by comparing with conventional top die casting barstock,and the mechanical properties of VHCC K418 are better than that of standard sample,revealing that VHCC technology could exploit the potential performance of alloy.It was analyzed that the characteristics of VHCC such as bottom casting,rapid solidification by water-cooled copper mould are the main reasons for high cleanliness and finer microstructure of K418 barstock,resulting in comprehensive im-provement of mechanical properties such as fatigue,stress rupture and tensile.

The phase transformation of high temperature and high strength alloy containing boron of 0.11wt％,and the effect of heat treatment on its microstructure were studied.The results show that,the as cast microstructure of the alloy is mainly composed of eutectic γphase,secondary γ'phase,γ/γ'phase and boride.During solution treatment,block-shaped secondary γ'phase and boride were dissolved in the matrix,and their sizes become smaller with increase of solution temperature;during aging treatment,tiny third γ'phase again separates out from the over saturated γphase,and the quantity increases with the increase of solid solution temperature.After 1120 ℃ ×4 h,AC+900 ℃ ×10 h,AC solution and aging treatment,the alloy can obtain the ideal microstructures of fine dispersed borides,and comprehensive strengthening phase of secondary and tertiary γ'phase.The tensile strength of the alloy at 800 ℃ can reach 1030MPa,and the alloy has good plasticity.