喷射成形工模具钢沉积坯中冶金缺陷计算分析及其消除

用有限元方法计算分析了喷射成形工模具钢沉积坯内部疏松等冶金缺陷的成因,并计算、验证了热等静压或锻轧等热加工消除内部缺陷的过程。研究表明,喷射成形工模具钢沉积坯粥状层补缩不足和冷却收缩产生的热应力是造成坯体中疏松等冶金缺陷的重要原因。热等静压采用的温度为1 170 ℃,锻造加工温度也能达到1 150 ℃,在这样温度下,工模具钢表现出一定的塑性,高温高压的热加工过程,对材料内部的冶金缺陷起到了一定的弥和作用。试验结果表明,经历热加工过程后的工模具钢内部的冶金缺陷明显减少。热等静压或锻轧等热加工可有效减少喷射成形工模具钢坯体内部的疏松等缺陷,热锻、热轧是消除沉积坯内部冶金缺陷的重要方法。另外,与Ar气相比,采用N2做雾化气体的喷射成形工模具钢沉积坯,由于高温下气体和合金元素的反应,沉积坯内部的含气式疏松很少。因此,采用N2喷射成形制备的工模具钢经热加工后,沉积坯密度更接近理论密度。     

结构材料喷射成形技术与雾化沉积高温合金

喷射成形是利用快速凝固方法直接制备金属材料坯料或半成品的先进材料制造技术 ,喷射沉积高温结构材料的冶金性能好、生产效率高、成本低 ,因而在近几年得到了迅速发展 .本项研究的主要目的是要通过喷射成形工艺参数的调整、最大限度地直接减少喷射成形坯中的孔隙度 ,进而得到优质坯料 .利用优化的雾化喷射沉积技术制备了多种高温合金沉积坯 ,沉积坯整体致密、晶粒细小、组织均匀、无宏观偏析、含气量低、力学性能提高 .还简要地比较了喷射成形高温合金与用常规铸锭冶金工艺和粉末冶金工艺制备高温合金的异同 ;总结了航空材料研究院喷射成形高温材料近年来的研究状况 ,包括专用高温材料喷射成形装置和技术及其应用 .     

热等静压对喷射成形高温合金组织和性能的影响

研究了热等静压工艺对喷射成形Ｋ１７和ＧＨ７４２两种高温合金显微疏松和室温拉伸性能的影响。结果表明，热等静压处理可以闭合坯件内的疏松孔洞，提高合金致密度，进而提高合金的强度和塑性。     

一种喷射成形难变形高温合金的组织研究EI北大核心

研究了喷射成形工艺对一种高铝钛比、难变形高温合金GH710组织的影响,结果表明:喷射成形工艺成功制备GH710沉积坯件,坯件经过热等静压和变形后,外观组织良好,合金组织细密,晶粒尺寸在45μm左右,具有非常强的晶粒抗长大能力,主要有两种尺寸的γ′相,数量较多,主要分布在晶界和晶内。     

2006喷射成形国际会议简介(4)——喷射成形高温合金,结语和编后感

关于喷射成形高温合金,在SDMA2006国际会议上有一个主题报告,题名是"成核铸造——一种可能制造高温合金大型坯的喷射沉积工艺"(Nucleated Casting——A Spray Deposition Process With the Potential to Produce Large Superalloy Ingots),作者是美国ATI Allvac的Robin M.Forbes Jones和GE全球研究中心的William T.Carter,Jr.     

快速凝固AlFeX耐热铝合金喷射沉积坯锻造成型工艺试验研究

喷射沉积AlFeVSi合金锭坯需要采用高温（450℃）锻压来实现致密化．通过沿不同取向锻压试验了解了喷射沉积坯及其压实坯的变形能力和锻造损伤情况，采用钢包套锻造工艺制备了完全致密化的喷射沉积Al-9．20Fe-1．37V-2．30Si合金锻件．通过金相、透射电镜、扫描电镜、力学性能检测等研究手段研究了锻造变形对喷射沉积A1FeVSi合金锻坯组织性能的影响．结果表明，喷射沉积AlFeVSi合金坯可以通过锻压变形实现致密化，达到冶金结合状态．喷射沉积AlFeVSi合金压实坯锻造道次压下率可以确定为20—40％，锻造加载方向最好是垂直于喷射沉积原坯沉积面，且需增加可塑性包套来限制侧表面的自由变形．采用钢包套自由锻造工艺可以在累积78％的压缩变形率条件下制备具有良好组织性能的锻造制品．     

多层喷射沉积技术的研究及进展

详细阐述了多层喷射沉积技术的产生及发展现状。多层喷射沉积技术与传统喷射沉积技术相比,在制备大型预成形坯件时冷却速度更大,工艺操作更简单,坯件表面精度更高。     

喷射成形颗粒增强金属基复合材料研究进展

喷射成形是将熔融金属雾化和沉积过程相结合,直接由熔融金属制备具有快速凝固组织特征坯体的新型金属材料成形工艺。被引入到非连续增强体金属基复合材料制备领域后,先后发展出了预混喷射成形、反应喷射成形和喷射沉积等工艺方法。介绍了上述颗粒增强金属基复合材料喷射成形工艺方法的基本原理、特点及研究现状。通过对比分析发现喷射沉积技术由于其成形条件限制较少,适用范围广等特点得到了更为广泛的发展,最后结合自身研究对传统喷射沉积技术进行了一定的改进,采用气体-增强颗粒两相流作为雾化介质以期获得提高雾化效率和改善增强颗粒分布均匀性的双重效果。     

喷射成形高温合金的研究与应用

喷射成形是一种近终形快速凝固技术,综述了喷射成形高温合金的研究和应用.研究表明,喷射成形高温合金成分均匀、无宏观偏析、晶粒细小、气体夹杂含量低,力学性能与粉末合金相当,高于变形合金,冷热加工性能明显改善,且成本较低.喷射成形高温合金技术通过20多年的发展取得了较大的进步,包括纯洁金属喷射成形(CMSF)和纯洁金属成核铸造(CMNC).喷射成形高温合金的应用主要是管件、环形件和盘件.最后对喷射成形涡轮盘材料FGH96组织作了初步的研究.     

喷射成形工艺过程数值计算的研究进展

主要介绍了国内外目前对喷射成形过程中3个重要工艺环节(即雾化过程、金属熔滴沉积坯凝固时的热传输以及沉积坯形状控制)数值计算的研究进展,同时简介了喷射成形工艺流程,并对喷射成形数值计算以后的发展提出了一些观点.     

镍基高温合金690的研究现状

690合金是一种面心立方结构的镍基高温合金,具有优异的高温力学性能和耐腐蚀性能,被广泛应用于核电、石油化工和航空航天等领域.文中对690合金的微观组织演化、热成形特性、高温失塑裂纹和耐应力腐蚀性能等方面的研究现状进行了总结分析.目前,部分合金元素对690合金组织性能的影响较为复杂,成形工艺参数对690合金高温变形行为和...     

大尺寸ZrO2注射成型坯体热脱脂缺陷成因探究

采用蜡基ZrO2粉末喂料注射成型获得大尺寸ZrO2陶瓷粉末注射产品（坯体）,并根据喂料热分析曲线的变化特点,系统研究了大尺寸ZrO2坯体的热脱脂过程及规律。通过对热脱脂前后坯体的重量损失、尺寸收缩、外观缺陷和微观组织形貌的分析评估,着重探讨了大尺寸ZrO2坯体热脱脂过程中存在的主要缺陷和成因。研究表明,流蜡、鼓泡和开裂等热脱脂缺陷主要发生在低温脱脂阶段,其主要原因是液态石蜡扩散及分解过程的失衡。为此,结合“失重率控制”的思路和喂料的热失重规律,对热脱脂工艺进行了优化,在不延长总脱脂时间的前提下,显著提高了大尺寸ZrO2坯体的脱脂合格率。     

Verallgemeinerungsfähige Merkmale und Besonderheiten des Sprühkompaktierens

Characteristic Features and Specific Qualifications of the Sprayforming Process to be Generalized The solidification and cooling process of spray formed materials predominates the extent of any segregation and separation process, which is conducive to avoid macro‐segregation and to diminish concentration of alloying components at the grain boundaries. The risk of coarse porosity or of hot cracking is reduced significantly by the momentum of the mass flow during spray deposition. This means that those materials which e.g. during the casting process tend to establish strong segregation effects and cavities and/or hot cracks as well as those which tend to create filaments of carbides, nitrides or sulphides during rolling can be generated by the spray forming process in large dimensions with chemical homogeneity and without any of those defects. A characteristic feature of spray formed materials is the fine equiaxed grain structure and the high ductility. Specific features of this new free forming process will be discussed.     

Analysis of material degradation for uncoated and NiCoCrAlY cold spray coated Superfer 800H in the secondary chamber of medical waste incinerator

NiCoCrAlY coating was deposited on Superfer 800H superalloy with cold spray process to reduce the degradation rate of substrate superalloy in actual medical waste incineration environment. Erosion–corrosion performance of uncoated and cold sprayed superalloy was evaluated in the secondary chamber of medical waste incinerator. The degradation rate of the specimens was assessed by measuring the thickness loss of the specimen after cyclic exposure for 1000 h in medical waste incineration environment. Average degradation rate for uncoated and cold sprayed superalloy was found to be 157.95 mpy and 36.56 mpy respectively. The better performance of cold spray coated specimen might be attributed to the formation of protective Al₂O₃ scale at the top of surface and dense structure of the deposit coating.     

Droplet velocity and thermal state from hot gas atomization of steel melt: Impact on the quality of the spray-formed tubular deposit

The velocity and thermal behavior (temperature, enthalpy, solid fraction) of atomized droplets in a metal spray play the most important role in the spray forming process. These properties mainly determine the materials yield and the final product quality (e.g., porosity, microstructure) of the as-sprayed materials. Changing the gas temperature in the atomization process directly influences these droplet properties in the spray. To understand the droplet behavior in the spray at various atomization gas temperatures (i.e., room temperature RT 293 K, 573 K, 873 K), numerical simulations using computational fluid dynamics (CFD) techniques have been performed and validated by experiments. A series of atomization runs (powder production and spray-forming with AISI 52100 steel) has been conducted at different atomization gas temperatures and pressures with a close-coupled atomizer (CCA). The in-situ temperature detection of the deposit surface (pyrometer) and in the substrate (thermocouples) has been performed to observe the effect of particle properties on the deposit. The result shows that hot gas atomization provides smaller droplets with faster velocity in the spray, affecting the droplet impact and deformation time in the deposition zone. A higher solid fraction of the smaller droplets by hot gas atomization also reduces the deposit surface temperature. Increasing the substrate diameter further decreases the deposit surface temperature without compromising the deposit quality (i.e., porosity) and also refines the grain size. Pre-heating of the substrate up to 573 K results in lower porosity in the vicinity of the substrate.     

A hybrid arc spray forming technique for the manufacture of nickel superalloy IN617

Spray forming produces cast microstructures with comparatively low macro‐ and micro‐structural chemical segregation and is thus well‐suited for the manufacture of complex chemistry, multi‐component alloys that otherwise show strong elemental segregation. Although spray formed Ni superalloys have shown properties equivalent or superior to their conventionally cast/wrought counterparts, they have not been adopted commercially because of the difficulties in ensuring a high process yield and the complexity and associated cost of large‐scale Ni superalloy melting. In this paper, we describe a hybrid arc spray forming (HASF) process in which costly, large‐scale alloy melting as pre‐cursor to spray forming is avoided by the use of a consumable wire feedstock. To achieve thermal conditions of melt spray forming – essential to produce a refined, polygonal grain structure – a customised secondary atomisation system has been developed. Fe‐0.8 wt%C and Ni superalloy IN617 microstructures and preliminary mechanical properties suggested that hybrid arc spray forming may offer an attractive combination of convenience, low cost and mechanical performance.     

Susceptibility to Hot Cracking and Weldment Heat Treatment of Haynes 230 Superalloy

This study investigates the susceptibility of hot cracking and weldment heat treatment of Haynes 230 superalloy. The Varestriant test was conducted to evaluate this susceptibility. Welding was performed by gas tungsten arc welding （GTAW） and plasma arc welding （PAW） with stress relief heat treatment and solid solution heat treatment. A tensile test is then performed to measure the changes in the mechanical properties of the heattreated material. The results indicate that the number of thermal cycles does not affect the susceptibility of Haynes 230 superalloy to hot cracking. However, it does increase the strain. In weldment of heat treatment, stress relief annealing increases the yield strength and tensile strength of the welded parts. The section of the tensile specimens shows fibrous fractures on the welded parts, regardless of whether they are heat-treated.     

M38合金表面防护涂层的热腐蚀行为

通过粉末包埋渗的方法在M38高温合金表面制备了4种改性铝化物涂层：NiCr-CrAI、Al-Si、Al-Ti和Co-Al涂层,对比研究了4种涂层在900℃下的涂盐（25％NaCl＋75％Na2SO4质量分数）热腐蚀行为。结果表明,4种改性的铝化物涂层中Al-Ti涂层抗热腐蚀性最好,腐蚀产物连续、致密;Al-Si涂层与Al-Ti涂层抗热腐蚀性相当,但腐蚀表面有局部剥落现象、氧化较严重;Co-Al涂层和NiCr—CrAl涂层抗热腐蚀性能依次降低,其中Co-Al涂层裂纹较严重,NiCr-CrAl涂层氧化较严重。     

Spray forming of high density sheets

Porosity is one of the most important quality criteria of spray‐formed materials in the as‐sprayed condition. Typically, spray‐formed sheets have a porous rim close to the substrate and depending on the spray conditions cold or hot porosity may also be present in the core of the deposit. This porosity has to be removed or minimized to make further processing steps such as rolling, forging or extrusion possible. In this paper, the influence of both substrate temperature and deposit surface temperature on porosity in spray‐formed sheets is studied. For this purpose spray forming experiments (sheet size 1000 mm × 250 mm) were carried out using three different materials: aluminium‐bronze, tin‐bronze and a nitriding steel. For the copper‐base alloys preheated steel‐substrates with different temperatures were moved through a scanning spray cone. In the case of steel a ceramic substrate at room temperature was used. In addition to the variation of the substrate temperature, the gas to metal mass flow ratio (GMR) was varied to achieve different deposit surface temperatures. During the run the surface temperature in the deposition zone was measured using a scanning, multi‐wavelength pyrometer. Samples of the deposits were polished and rasterized by light microscopy. The local porosity was characterized by digital image analysis. The influence of the substrate temperature and the GMR on the porosity in the vicinity of the substrate is evaluated and discussed in detail. The impact of the deposit surface temperature on the porosity was analyzed and is discussed as well. It was found that the deposit surface temperature has a strong impact on porosity for spray‐formed sheets. Finally, experimental results were used to develop a new approach to predict the porosity in spray‐formed sheets. The results clearly show the dependence on material properties. This approach can be used to identify process parameters to generate high density sheets in the future.     

Influence of Ti content on microstructure,mechanical properties and castability of directionally solidified superalloy DZ125L

Directionally solidified DZ125L alloys of various Ti content were developed by low segregation technology. The microstructure, mechanical properties and castability of directionally solidified superalloy DZ125L were investigated. With decreasing Ti content in DZ125L alloy, the size, volume fraction and separation temperature of γ′ decreased. While the tensile strength and rupture life of directional solidified cylindrical samples is also obviously decreased. Lowering Ti content in alloy resulted in free hot cracking casting blades. Compared with IN792 alloy, DZ125L alloy needs much lower Ti/Ta ratio to achieve good castability.