Recent research progress in the mechanism and suppression of fusion welding-induced liquation cracking of nickel based superalloys

Nickel-based superalloys are extensively used in the crucial hot-section components of industrial gas turbines,aeronautics,and astronautics because of their excellent mechanical properties and corrosion resistance at high temperatures.Fusion welding serves as an effective means for joining and repairing these alloys;however,fusion welding-induced liquation cracking has been a challenging issue.This paper comprehensively reviewed recent liquation cracking,discussing the formation mechanisms,cracking criteria,and remedies.In recent investigations,regulating material composition,changing the preweld heat treatment of the base metal,optimizing the welding process parameters,and applying auxiliary control methods are effective strategies for mitigating cracks.To promote the application of nickel-based superalloys,further research on the combination impact of multiple elements on cracking prevention and specific quantitative criteria for liquation cracking is necessary.

Liquation cracking in laser beam welded joint of ZK60 magnesium alloy

The ZK60 magnesium alloy plates were welded by laser beam welding (LBW) and the microstructures in the partially melted zone (PMZ) of welded joints were investigated. For the as-cast alloy, the eutectoid mixtures along grain boundaries (GBs) in the PMZ are liquefied during welding, and their re-solidified materials present hypoeutectic characters, which lead to more severe segregation of the Zn element along GBs, and thus enhance the cracking tendency of the PMZ. The main reasons for liquation cracking of PMZ are described as that the absence of liquid at the terminal stage of solidification leads to the occurrence of shrinkage cavities in PMZ, from which liquation cracking initiates, and propagates along the weakened GBs under the tensile stress originating from solidification shrinkage and thermal contraction. Lower heat input can reduce the cracking tendency, and the plastic processing such as rolling also contributes to the mitigation of PMZ liquation cracking by reducing the size of eutectoid phases and changing their distribution in the base metal.

Weldability and liquation cracking behavior of ZhS6U superalloy during electron-beam welding

The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding(EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatment cycles on the final microstructure before and after welding were examined. Welds were made on flat coupons using an EBW machine, and the two heat-treatment cycles were designed to reduce γ′ liquation before welding. Microstructural features were also examined by optical and scanning electron microscopy. The results showed that the change in the morphology and size of the γ′ precipitates in the pre-weld heat-treatment cycles changed the ability of the superalloy to release the tensile stresses caused by the matrix phase cooling after EBW. The high hardness in the welded coupons subjected to the first heat-treatment cycle resulted in greater resistance to stress release by the base alloy, and the concentration of stress in the base metal caused liquation cracks in the heat-affected zone and solidification cracks in the weld area.

Liquation cracking in the heat-affected zone of IN939 superalloy tungsten inert gas weldments

The main aim of this study was to investigate liquation cracking in the heat-affected zone(HAZ)of the IN939 superalloy upon tungsten inert gas welding.A solid solution and age-hardenable filler metals were further studied.On the pre-weld heat-treated samples,upon solving the secondaryγ′particles in the matrix,primaryγ′particles in the base metal grew to"ogdoadically diced cubes"of about 2μm in side lengths.The pre-weld heat treatment reduced the hardness of the base metal to about HV 310.Microstructural studies using optical and fieldemission scanning electron microscopy revealed that the IN939 alloy was susceptible to liquation cracking in the HAZ.The constitutional melting of the secondary,eutectic,and Zr-rich phases promoted the liquation cracking in the HAZ.The microstructure of the weld fusion zones showed the presence of fine spheroidalγ′particles with sizes of about 0.2μm after the post-weld heat treatment,which increased the hardness of the weld pools to about HV 350 and 380 for the Hastelloy X and IN718 filler metals,respectively.Application of a suitable solid solution filler metal could partially reduce the liquation cracking in the HAZ of IN939 alloy.

Microstructure characteristics and liquation behavior of fiber laser welded joints of Mg-5Zn-1Mn-0.6Sn alloy sheets

Fine-grained Mg?5Zn?1Mn?0.6Sn alloy sheets of2mm in thickness were welded by fiber laser welding.The appearanceand microstructures of the welding joints and liquation behaviors in the partially melted zone(PMZ)were investigated.The resultsshow that,with the lower welding power and higher welding speed,the width and depth of the joints decrease.Moreover,some poresare detected at a very high welding speed.There are two kinds of liquation phenomena in the PMZ.One is the liquation networkalong grain boundaries associated with the liquation of substrate and segregation-induced liquation,the other is the molten poolinvolved with the liquation of the residual second phases at the boundaries.However,the liquation of substrate and thesegregation-induced liquation are the main liquation mechanism in the PMZ.

EXPERIMENTAL RESULTS OF LIQUATION OF TUNGSTEN-AND TIN-BEARING GRANITIC MAGMAS SATURATED WITH WATER AND THEIR METALLOGENIC SIGNIFICANCE

Systematical experimental study has been carried out on liquation (liquid seperation) of granitic silicate melt containing tungsten and tin at the conditions of 850℃ and 150 MPa. The experiments were conducted in rapid quenched high-pressure vessel system.Two kinds of glass, used as starting meterial, were made from Dengfuxian coarse porphyritic biotite granite enriched in W (0. 45 wB% ) and Sn (0. 50 wB%) and Dachang granular biotitemuscovite granite enriched in W (0. 16 wB% ) and Sn (0. 13 wB%). The results of the experiments indicate that the quenched product glass contains no newly-formed minerals through observation under 200 times microscope and with determination of the X-rays diffraction. The final glass of each run consists of both lightedolor and dark-color parts which represent two phases of liquid-separated melt. The color of the light gIass varies with the composition of the systems. In the granite-KF-H2O and granite-NaCl-H2O systems, the light glass is colorless.In the granite-KP-H2O system, the light part is lightly brown. In the Rranite-LiF-H2O system, the light glass appears milkwhite. The color of the dark glass hardly varies with the different compositions of the systems, and appears darkbrown or grew-black. In tbe quenched glass, the dark part is dominant and takes a portion of more than 80 percent. The data of the compositions for the two portions of glass contains relatively much silica and less Fe2O3,FeO, TiO2, MgO, CaO. On the contact line between two phases of glass, there does not exist gradually varying zone of the composition, which indicates that complete liquid separation has taken place.

龙眼核淀粉的液化及糖化工艺优化

为探究龙眼核发酵酿制保健酒原料预处理方式,对龙眼核淀粉酶解工艺进行优化。采用中温α-淀粉酶和糖化酶对龙眼核粉进行酶解处理,以还原糖含量为评价指标,通过单因素试验和正交试验优化酶解工艺条件,并比较了双酶协同酶解和两步酶解的效果。最终确定双酶协同酶解法效果优于两步酶解法,其最佳工艺条件为40 U/g中温α-淀粉酶和180 U/g糖化酶、pH6.0、酶解温度65℃、酶解时间120 min。在此条件下还原糖含量为75.93%,与两步酶解法相比,其还原糖含量高44.94%,时间缩短80 min。

异质镍基高温合金激光沉积修复开裂机理研究

针对高裂纹敏感性K424镍基高温合金薄壁件难修复现状,采用低裂纹敏感性的GH4169镍基合金粉末在K424高温合金基板上进行激光沉积修复,对过程中产生的裂纹特征和开裂机理进行了研究。结果表明:修复时,裂纹首先在基材的热影响区萌生,然后分别向沉积区和基材内部扩展。这些裂纹呈现出曲折的沿晶界开裂特征,具有典型的液化裂纹形貌。经形貌分析和成分分析发现,晶界上的液膜主要来源于晶界上较大尺寸的在激光作用下未完全熔解的γ'相与γ相发生共晶反应,在热作用下形成液膜。此外,碳化物、硼化物等低熔点相在高温下熔解发生富集,促进了高温下液膜的形成。通过Simufact Welding软件所建立的数值模型验证了修复过程中的应力场和温度场,其中热影响区附近存在较大的应力场,是裂纹形成的驱动力。因此,在热影响区内,晶界上液膜的产生和较大应力的存在为液化裂纹的形成提供了条件。

电解金属锰制液过程中的氧化锰除铁工艺优化

电解金属锰制液工艺中,常利用氧化锰粉将Fe^(2+)氧化成Fe^(3+),以便在后续中和过程中形成氢氧化铁胶体,实现铁的去除。针对低品位氧化锰粉在生产过程中存在除铁利用率低的问题,开展了氧化锰粉除铁工艺优化研究,结果表明:当除铁锰粉粒径≤125μm,初始酸的质量浓度为6.5 g/L,反应温度为60℃,反应时间为90 min时,除铁利用率达到98.4%,实现除铁氧化锰粉的高效利用。

金平普角钴金多金属矿地质特征及矿床成因浅析

普角钴金多金属矿位于金平县城南西方向,平距约25 km,矿区包括老刘寨矿段和期腊矿段,目前已在老刘寨矿段探获1条钴矿化体,赋存于橄榄岩中,为岩浆熔离型钴矿体;在期腊矿段探获3条含金银铜铅多金属矿化体,矿化体均为受构造裂隙或破碎带控制的含硫化物石英脉型矿体。区域成矿地质条件优越,矿区内展现出较好的找矿潜力。通过对成矿地质背景、矿床地质特征、矿化蚀变特征总结,浅析矿床成因,为找矿思路提供理论支撑。

Geohazards Induced by the Lushan Ms7.0 Earthquake in Sichuan Province, Southwest China:Typical Examples, Types and Distributional Characteristics

Geohazards induced by the Lushan Ms 7.0 earthquake on April 20, 2013 mainly have four types： collapse, landslide, slope debris flow, and sand-soil liquefaction. These geohazards mainly occurred near the epicenter, on steep slopes or below cliffs in high mountain and deep valley areas, and at or near fault ends. They have no obvious relationships to active faults, but their relationships to the weathering degree and structures of rock and rock mass are obvious. Compared with the Wenchuan Ms 8.0 earthquake on May 12, 2008, the Lnshan earthquake is relatively little in the impact force and the throwing amount. All of these should be related to the magnitude of this earthquake, not very large but not very little. This character of the Lushan earthquake would make some processes uncompleted so as to bring about some concealed geohazards. Finally, in order to deal with challenges presented by such conceal geohazards, some brief recommendations are put forward.

碳化钨颗粒在WC/Fe基复合材料基体中的断裂和熔解

利用V-EPC铸渗法制备了碳化钨颗粒增强铁基表面复合材料,结合差热分析测试,研究了碳化钨颗粒在基体中的断裂和熔解。结果得出,在铸渗过程中,温度的急剧变化所产生的热应力导致碳化钨颗粒在基体中发生断裂,而原始碳化钨颗粒的表面尖角促使其与基体间界面的平衡熔点降低,从而导致碳化钨颗粒发生熔解。结果还得出,可以通过改善碳化钨颗粒的导热性能和减少其显微缺陷来阻止碳化钨颗粒在基体中的断裂,同时可以通过控制原始碳化钨颗粒的表面质量和浇注温度来控制碳化钨颗粒在基体中的熔解。

Low-temperature purification process of metallurgical silicon

The removal of B and P consumes most of heat energy in Si metallurgical purification process for solar-grade Si. Metal-liquating purification of metallurgical grade silicon （MG-Si）, also called Si-recrystallization from metal liquid, was a potential energy-saving method for the removal of B and P efficiently, since Si could be melted at lower temperature by alloying with metal. The selection criteria of metal-liquating system was elaborated, and Al, Sn and In were selected out as the optimum metallic mediums. For Sn-Si system, the segregation coefficient of B decreased to 0.038 at 1 500 K, which was much less than 0.8 at the melting point of Si. The mass fraction of B was diminished from 15×10^-6 to 0.1×10^-6 as MG-Si was purified by twice, while that of most metallic elements could be decreased to 0.1×10^-6 by purifying just once. During the metal-liquating process, the formation of compounds between impurity elements and Si was also an important route of impurity removal. Finally, one low-temperature metallurgical process based on metal-liquating method was proposed.

3S技术在天然气液化中的应用初探

通过建立低温下3S分离器的一维稳定流动数学模型,对采用3S分离器的天然气液化流程进行了探索性的理论研究。结果表明采用3S分离器的液化技术效率远高于J-T阀,其液化率与采用膨胀机相当,由于3S分离器不仅可带液工作,且无运动件,在小型天然气液化装置中有广阔的应用前景,但需解决一系列技术问题。

加热工艺对轴承钢连铸坯液析碳化物溶解行为的影响

利用DICTRA软件及金相法对GCr15轴承钢连铸坯中的液析碳化物在加热工艺中的溶解与扩散机理进行研究,并针对常规加热工艺存在的问题,提出加热工艺的设计思路：第一阶段在液析严重区域连铸坯的固相线温度以下进行加热,加热过程中仅发生液析碳化物的溶解,令C元素快速扩散,同时该区域固相线温度逐渐升高;第二阶段在1200～1280℃的高温区进行加热,由于第一阶段中液析严重区域连铸坯的固相线温度升高,此时很难再有液相增加,可保证Cr元素快速扩散,最终令液析碳化物快速溶解扩散。根据DICTRA软件对加热工艺的模拟计算结果,设计加热工艺为＂1100℃加热1 h后1250℃加热1 h＂。以该工艺对试样进行加热试验,液析碳化物级别由4.0级降低至0.5级,结果证明了该加热工艺的可行性。

北山裂谷红石山镍矿床特征及成因——多期岩浆成矿作用

新疆东天山南部北山裂谷带中出露大量镁铁-超镁铁岩,铜镍含量较低。红石山镍矿位于北山裂谷金铜镍成矿带西部,在前人工作基础上,结合裂谷环境下成岩机制,对红石山铜镍矿矿区侵入岩序列、容矿围岩及构造、矿体特征进行研究,分析红石山铜镍矿成矿环境及成矿作用演化特征,建立多期岩浆成矿模式及找矿标志,以期为矿区寻找隐伏矿床(体)及铜镍矿床提供理论依据。

镍基高温合金电子束焊接热影响区微裂纹特征分析

利用金相分析和扫描电镜对镍基高温合金电子束焊接热影响区微裂纹行为进行了分析。研究发现,熔合线附近的热影响区产生大量液化裂纹和沿晶扩展的固相裂纹。液化裂纹起源于MC碳化物的组份液化而形成的晶界连续或半连续的低熔点共晶液化膜,固相裂纹形成的则是高能电子束流的快速瞬态热冲击效应的直接结果。通过改善焊缝成形和提高焊接线能量有助于减小两类热影响区微裂纹倾向。

硅锰装甲钢破甲弹坑损伤与微观结构关系的研究

利用ＳＥＭ和光学金相研究了４３лＣＭ钢破甲弹坑内损伤与材料微观结构之间的关系。认为，损伤主要发生在：（１）绝热剪切带上，损伤的形式多为孔洞和微裂纹，孔洞的分布和形貌表明，它是在绝热剪切的“高温”状态下，通过快速形核、长大而形成的；（２）靶板的轧制偏析带和夹杂物处，损伤的形式以微裂纹为主，这些微裂纹常通过剪切带聚合成梯形波裂纹。

小岩体成大矿与岩浆通道成矿理论的比较

从小岩体成大矿和岩浆通道成矿理论的提出、发展、完善及其主要成矿控制因素展开探讨,结合典型矿床实例,指出这两种理论在勘查实践中的贡献和应用价值,并比较其异同点。小岩体成大矿与岩浆通道成矿理论的主要区别在于:小岩体成大矿理论中岩浆管道与岩浆通道成矿理论并非同一概念;深部熔离预富集是前者的主要控制因素;前者是硫化物深部熔离-脉冲式贯入占主导,而后者是硫化物就地熔离-局部聚集为主;在硫化物熔离机制方面,后者要求外来硫的加入是必需条件,而前者认为外来硫的加入并非不可或缺,在岩浆深部就可以发生硫化物不混溶作用;在成矿物质聚集方式上,后者认为含矿岩浆分凝和上侵是连续过程,而前者则强调岩(矿)浆上侵是脉动式过程。在找矿实践过程中要重视小岩体,并注重含矿小岩体的下盘和岩浆上升的管道位置,这些地区是扩大区域找矿前景、增加资源储量最具潜力的部位。

喀喇沁玻基橄辉岩中的磷酸盐质熔体及磷灰石

磷酸盐在本文讨论的玻基橄辉岩中以多种形式产出 ,有早期结晶的磷灰石斑晶 ;有熔离的磷酸盐质熔浆液滴 ;也有晚期穿入橄榄石斑晶的磷酸盐质细脉 ,表明元素磷活跃在岩浆演化的每一个阶段。磷酸盐质熔浆液滴的存在 ,说明磷酸盐质熔体可能是由于岩浆的熔离作用而形成的。沿着橄榄石晶格生长面出现的磷酸盐质玻璃细脉则进一步证实地幔中含磷流体不但存在 。