镁合金回收用坩埚失效原因分析

镁合金回收静置炉坩埚在使用3个～4个月后，坩埚底壁厚减薄严重过早报废.用ICP-AES和金相显微镜对坩埚底物质观察、分析用SPARK发射光谱仪对坩埚中不同深度镁合金液体成分进行分析，结合生产制程分析其失效原因.结果表明，由于沉降作用，在坩埚底部容易形成一层含铝、锰、铁金属间化合物的富铝层，富铝层很容易和坩埚基体发生反应，生成硬脆的金属间化合物；金属间化合物的不断剥落，使得坩埚基体有效壁厚减小很快，最终导致坩埚提前报废.     

Al—SiC复合材料铸造发展概况

一、“Duralcan”铝复合材料 铝—陶瓷复合材料已有20多年历史,它具有良好的抗拉性能,尤其是具有较高的比强度(刚性),已在汽车、航空和国防工业上应用,这些金属陶瓷复合材料(MMC),不能采用熔铸方法制造,一般采用粉末冶金、热喷涂、热扩散或高压挤压工艺生产金属基体复合材料的零件。1986年以前尚未采用铸造方法生产金属基体陶瓷复合材料。 用于铸造的金属陶瓷复合材料必须满足以下三个基本条件:     

抗铝液侵蚀坩埚材料的试验研究

分析不锈钢、球墨铸铁、灰口铸铁、过共析钢等金属材料的组织结构，研究了材料组织结构对抗铝液侵蚀能力的影响，试验得出各种材料抗铝液侵蚀能力比较数据。在此基础上设计陶瓷-金属表面复合材料，讨论了构成陶瓷-金属表面复合材料的方法和工艺，用陶瓷中的Al2O3成分抵抗铝液对母体金属的侵蚀。试验结果证明，该方法可以显著提高材料的抗铝液侵蚀的能力。     

热压制备的颗粒增强铝基复合材料的磨损特性

对热压制备的Ａｌ２Ｏ３、ＳｉＣ颗粒增强纯铝基复合材料的磨损行为的研究表明，复合材料的耐磨性均于基体金属，且随着颗粒含量的增加，复合材料的耐磨性提高，陶瓷颗粒的加入是复合材料耐磨性提高的主要原因。     

铝基陶瓷增强复合材料的钎焊及扩散焊

由于陶瓷增强相与金属基体合金性能的巨大差异,造成铝基陶瓷增强复合材料的焊接困难较大.在各种焊接方法中,钎焊和扩散焊是铝基陶瓷增强复合材料焊接比较常用的方法.本文研究了钎料和中间层合金与铝基复合材料的润湿机理,介绍了颗粒增强铝复合材料的超声波钎焊、真空钎焊、无夹层液相扩散焊、冲击扩散焊和瞬时液相扩散连接等焊接新工艺,对这些焊接工艺的原理与特点进行了探讨.     

粉煤灰泡沫陶瓷铝基复合材料凝固组织的研究

以粉煤灰泡沫陶瓷为增强体,基体材料为Al-Si共晶铝硅合金和Al-23Si过共晶铝硅合金,采用压铸工艺制备了泡沫陶瓷铝基复合材料.通过光学金相分析,研究了不同浇注温度下,复合材料的界面结合以及泡沫陶瓷骨架对材料凝固组织的影响.结果表明:随着浇注温度的升高,铝合金的充型能力提高,但晶粒尺寸也会增加;共晶铝硅合金与过共晶铝硅合金均能制备出界面结合良好的复合材料:泡沫陶瓷骨架对两种基体合金凝固时均有形核基底的作用.     

SiC_P/Al复合材料导热性能研究

采用铝液无压浸渗工艺制备了SiCP/Al复合材料,研究了基体金属、颗粒粒径、颗粒体积分数、颗粒形貌对复合材料导热性能的影响。结果表明,以ZL101为基体的该复合材料的热导率高于以纯铝1060为基体的热导率,以纯铝1060为基体的SiCP/Al复合材料存在Al4C3。SiCP/Al复合材料的热导率随SiC颗粒粒径增大而增大,而颗粒体积分数越高,复合材料的热导率越低。近球形SiC颗粒增强复合材料的热导率高于不规则形颗粒增强复合材料的热导率。     

粉煤灰泡沫陶瓷铝基复合材料耐磨性能的研究

从摩擦时的转速、磨损时间、摩擦副的表面粗糙度和载荷等方面研究这些因素对复合材料耐磨性的影响,研究了粉煤灰泡沫陶瓷复合材料及基体材料的抗磨损性能。结果表明,粉煤灰泡沫陶瓷复合材料具有较高的耐磨性,其耐磨性明显高于基体,该复合材料抵抗磨损的性能比基体材料增加了3～4倍。     

陶瓷粒子增强的锌铝基复合材料的摩擦学特性

以陶瓷颗粒碳化硅、氮化硅、三氧化二铝为增强体，锌铝合金ZA-27为基体，通过对陶瓷颗粒进行预处理、机械搅拌和合金化等技术，将陶瓷颗粒与熔融状态的锌铝合金复合成均匀的浆料，用挤压铸造法挤压成型，得到陶瓷颗粒锌铝合金复合材料铸件。在金属基体上，均匀分布着陶瓷颗粒。在有润滑和无润滑的情况下，复合材料的耐磨减摩性能均比ZA-27有较大幅度提高。     

BN/Al金属基复合材料

ＢＮ／Ａｌ金属基复合材料陶瓷增强剂与其金属基体之间的良好结合，是获得金属基复合材料高强度的关键，但是通常由于金属与陶瓷在物理、化学、电学以及力学性能上的差异，而很难获得良好的结合，采用传统的粉末冶金法就得不到性能良好的ＢＮ／Ａｌ金属基复合材料。近年来...     

Effect of Impact Angle on Ceramic Deposition Behavior in Composite Cold Spray: A Finite-Element Study

During the cold spraying of particle-reinforced metal matrix composite coatings (ceramic and metal particles mixture) on metal substrates, ceramic particles may either get embedded in the substrate/deposited coating or may rebound from the substrate surface. In this study, the dependence of the ceramic rebounding phenomenon on the spray angle and its effect on substrate erosion have been analyzed using finite-element analysis. From the numerical simulations, it was found that the ceramic particle density and substrate material strength played the major roles in determining the embedding and ceramic retention behavior. Substrate material erosion also influenced the ceramic retention, and the material loss increased as the impact angles decreased from normal. In general, the results concluded that decreasing the impact angle promoted the retention possibility of ceramics in the substrate. This study provides new theoretical insights into the effect of spray angles on the ceramic retention and suggests a new route toward optimizing the spraying process to increase the ceramic retention in composite coatings cold spray.     

Interactions between TiAl alloys and yttria refractory material in casting process

In this work, U-shaped yttria ceramic crucibles have been prepared to melt Ti–47Al (at.%) alloy in a vacuum induction furnace, in order to simulate the worst practical situation with respect to the interactions between TiAl alloy and yttria refractory material. The effects of superheating temperature and cooling media on the metal–crucible interface, microstructure, chemical composition and microhardness have been evaluated. The investigation demonstrates that interactions between the yttria crucible and the molten TiAl consist of slight chemical dissolution and some physical erosion and the extent of the dissolution and erosion depend on the superheating temperature. The thermodynamics of TiAl–Y₂O₃ reactions have been investigated according to the calculation of the Gibbs free energy change of the yttria dissolution reaction. The possibilities of melting and casting TiAl alloys by the use of yttria refractory material are also discussed.     

坩埚设计对多晶硅铸造应力的影响

针对铸造多晶硅凝固膨胀产生的应力引起铸锭开裂的问题,采用自行设计的分体式坩埚作为浇注模进行实验,与普通坩埚进行对比,并对裂纹形成机理进行了分析。结果表明,采用普通坩埚浇注的铸锭产生明显的宏观裂纹,而采用分体式坩埚浇注的铸锭没有裂纹;另外,普通坩埚只能使用一次,分体坩埚可重复使用。     

Microstructure and mechanical properties of cast Ti-47Al-2Cr-2Nb alloy melted in various crucibles

The main factors limiting the mass production of TiAl-based components are the high reactivity of TiAl-based alloys with the crucible or mould at high temperature.In this work,various crucibles (e.g.CaO,Y2O3 ceramic crucibles and water-cooled copper crucible) were used to fabricate the Ti-47Al-2Cr-2Nb alloy in a vacuum induction furnace.The effects of crucible materials and melting parameters on the microstructure and mechanical properties of the alloy were analyzed by means of microstructure observation,chemical analysis,tensile test and fracture surface observation.The possibilities of melting TiAl alloys in crucibles made of CaO and Y2O3 refractory materials were also discussed.     

球墨铸铁件表面片状石墨层的应用

球墨铸铁具有较佳的高温强度,灰口铸中片状石墨对铝合人具有抗蚀性;利用片状石墨可防止铝液侵蚀金属基体的特性,设计制作表面为灰口铸件材质的热电偶保护,使控温热电偶不因熔液溶穿保护管而损坏。     

Physical erosion of yttria crucibles in Ti–54Al alloy casting process

Y₂O₃ crucibles with different porosities were manufactured to investigate the physical erosion during the casting of Ti–54Al (at%) alloys. The effects of multiple superheating times on the chemical composition of the casting, the introduction of inclusions into the alloy and on the metal–crucible interface were studied. A large number of ceramic inclusions were introduced by the physical erosion of the crucible walls in contact with the molten alloy. The mechanisms by which the physical erosion was reduced are discussed in relation to the crucible wall permeability coefficient A′. By reducing the porosity content of the crucible, which led to a decrease of A′, the net increments of oxygen of the remelted Ti–Al as-cast samples were limited to a minimum level at 1873 K.     

Evaluation of crucible and investment materials for lost wax investment casting of Ti and NiTi alloys

Abstract

The aim of this study is to assess the suitability of selected commercial ceramic crucibles for the investment casting of Ti6Al4V and NiTi alloys for jewellery purposes. A commercial vacuum tilt casting machine and a centrifugal casting machine were employed to cast the alloys in cold copper moulds or in refractory investment shells. The form filling of the shell and the crucible and investment reactions were assessed by microstructural investigation, chemical analysis and hardness profiles of the as cast items as a function of shell temperature. The reaction of the alloys strongly depended on the alloy, the crucible material, the coating of the crucibles and the temperature of the ceramic shell. Optimum results were achieved with yttria and yttria coated Al titanate crucibles for Ti6Al4V and NiTi alloys respectively. Improvement of the materials and process costs is necessary to allow the competitive casting of jewellery made from titanium alloys.     

铅铋合金提纯用316L坩埚失效行为分析

使用316L坩埚对铅铋合金进行提纯处理6~7个月后,坩埚底部出现穿孔现象,侧壁减薄明显。利用XRD、SEM-EDS、LCM和体视显微镜对失效316L坩埚表面形貌、截面组分进行观察分析,结合使役环境分析失效原因。结果表明:在600 ℃待提纯液态铅铋合金中,316L坩埚发生严重的溶解腐蚀和氧化腐蚀;表面形成能有效保护基体的不均匀氧化层;未被氧化层保护的区域Sb元素富集,基体材料以大块物质剥落的形式进行溶解;基体内部出现蚀孔,蚀孔达到临界尺寸或在外力作用下,边缘处裂纹形核并长大,Sb元素沿裂纹扩展通道向基体内部渗透富集并溶解基体。     

碳气氛中熔炼金属时控制碳污染研究

进行碳气氛中陶瓷坩埚、带喷涂涂层石墨坩埚熔炼纯铁、铀、轴铌合金工艺试验，结果表明，与不带盖熔炼比较，坩埚带盖熔炼可有效降低铸锭碳增量。     

超硬磨具用金属结合剂国内外研究进展

金属结合剂超硬磨具广泛应用于石材、陶瓷和硬质合金的加工领域。介绍了目前常用的钴、铜、铁基等纯金属结合剂的特点、类型和力学性能。分析了不同添加物对金属–陶瓷复合结合剂性能的影响。重点阐述了近些年发展起来的金属–树脂复合结合剂的发展状况及趋势。最后提出了金属基复合结合剂发展中存在的问题。