Microstructure and Mechanical Properties of Electroslag Strip and Explosively Clad Low Alloy Steel: Stainless Steel Joints

The surface properties such as wear, corrosion, oxidation resistance etc., can be improved by using suitable cladding technique. The most commonly used cladding material is stainless steel for cladding on carbon and low alloy steel base materials. Mechanical properties are considered important for satisfactory performance of clad joints used in several defence applications. In this work, cladding of a high strength low alloy steel with stainless steel was carried out using explosive cladding and electroslag strip cladding processes. The relationship between mechanical properties and microstructure of clad materials was evaluated. The bond interface in explosively clad material shows a wavy interface compared to strip clad interface. Electron probe microanalysis revealed that inter-diffusion of elements was significant in strip clad joints and insignificant in explosively clad joints. Shear strength, notch tensile strength and impact toughness of explosive clad joints are much superior compared to those in strip clad joints.     

Lithium depletion during heat treatment of aluminum-lithium alloys

The loss of lithium from the near surface region during heat treatment of two commercial aluminum-lithium alloys was studied using a nuclear reaction analysis technique. A finely collimated 2.5 MeV beam of³He ions was used to stimulate the⁷Li(³He,p)⁹Be reaction in samples of BAACo 8090 and 8091 alloys heat treated for 1, 4, and 16 hours at 500 °C. The emitted protons were detected as a cross section of the sample was traversed through the beam, thereby determining the lithium content as a function of distance from the external surface. Suitable calibration and control samples were used to validate the technique. The lithium concentration data were fit with assumed concentration profiles calculated from diffusion equations and modified for the particular experimental configuration employed. Extensive lithium depletion was found in both alloys, and the concentration profiles were found to be accurately predicted by the diffusion calculations. For heat treatment in either wet or dry air, the depth of lithium loss was the same, and can be approximately given as x = 1.5 √Dt. When heat treated in an argon atmosphere, the depth of lithium loss was reduced. The lithium loss appeared to be limited by the diffusive flux of lithium to the surface of the sample in wet and dry air, but was limited by other factors in argon. Porosity was observed in the lithium depleted region; this was ascribed to the accumulation of vacancies generated by the unequal fluxes of aluminum and lithium atoms.     

三元硼化物金属陶瓷覆层材料耐腐蚀性能研究

以Mo粉、FeB合金粉和Fe粉为基本原料，分别加入Cr、Ni、C或同时加入Cr、Ni、C合金元素成分，采用原位反应真空液相烧结工艺，在Q235钢基体上制备三元硼化物金属陶瓷覆层材料。研究了合金组分对覆层材料耐腐蚀性的影响。结果表明，三元硼化物金属陶瓷覆层材料的覆层具有远比钢基体优越的耐蚀性，C组分的单独加入降低了覆层的耐蚀性，Cr、Ni组分的加入显著提高了覆层的耐蚀性，同时加入Cr、Ni、C作为合金组分使覆层具有最佳的耐蚀性。     

激光功率对碟阀表面熔覆Ni 基合金涂层性能的影响

采用半导体激光器在2205双相不锈钢表面激光熔覆Ni基合金涂层.借助扫描电镜、电化学综合测试仪和硬度测试仪等,探讨了激光功率对涂层稀释率、微观组织、耐腐蚀性能及硬度的影响.结果表明:激光功率越大,涂层稀释率越大,熔覆层与基体元素发生更多的对流扩散;熔覆层的耐腐蚀性能随激光功率的增加而降低,当激光功率为2.7 kW时,熔覆层的自腐蚀电位最低,为-0.46 mV,腐蚀电流最小,为3.47×10-5 A/cm2. 硬度测试实验表明,激光熔覆Ni基合金涂层硬度最高达680 HV,约为基体硬度的2.5倍.      

钛铝合金表面熔覆涂层的制备及组织特征

针对现有熔覆基体与熔覆层结合不紧密、工艺参数难以控制的缺陷,采用高功率连续CO2横流激光器及配套数控加工系统,实现了将Ni60B合金粉末均匀密实地熔覆在钛铝合金表面的方案。结合扫描电镜、金相分析、硬度测试等手段研究了输出功率、扫描速度对熔覆层组织和性能的影响。研究发现,基体材料与熔覆层之间存在明显的合金元素扩散现象,熔覆层与基体结合紧密;当激光功率为4.0 Kw,扫描速度为100 mm·min-1时,熔覆层的硬度达最高达HV 900以上。     

Thermal oxidation behavior of an Al-Li-Cu-Mg-Zr alloy

The chemical composition of oxide films formed during thermal treatments of an Al-Li-Cu-Mg-Zr alloy has been studied by means of Auger electron spectroscopy and X-ray photoelectron spectroscopy. The oxide layers formed after oxidation of 2.5 minutes to 30 minutes at 530 °C in lab air have been characterized. In the early stages of oxidation the surface is composed of both the lithium rich oxides and magnesium rich oxides. However, after longer oxidation times the oxidation of lithium becomes predominant and the air/oxide interface is completely covered by lithium compounds. Oxidation products formed on the alloy surface have been studied by X-ray diffraction analysis. The following three phases, namely, Li₂CO₃, α-Li₅AlO₄, and γ-LiAlO₂, were identified. During heat treatment in lab air at 530 °C and at atmospheric pressure the dominating reaction product is Li₂CO₃. Due to the selective oxidation of lithium a soft surface layer is developed. The width of the soft layer formed during solution heat treatments carried out in lab air and in salt bath environments has been determined by microhardness measurements. The lithium concentration profiles were calculated from a diffusion equation. The depletion of alloying elements from the near surface region during heat treatments has been investigated using energy dispersive X-ray analysis. The oxide morphology was examined using scanning electron microscopy and optical microscopy.     

Formation of intermetallic compound at interface between rare earth elements and ferritic-martensitic steel by fuel cladding chemical interaction

The intermetallic compounds formation at interface between rare earth elements and clad material were investigated to demonstrate the effects of rare earth elements on fuel-cladding chemical interaction(FCCI)behavior.Mischmetal(70Ce-30La)and Nd were prepared as rare earth elements.Diffusion couple testing was performed on the rare earth elements and cladding(9Cr2W steel)near the operation temperature of(sodium-cooled fast reactor)SFR fuel.The performance of a diffusion barrier consisting of Zr and V metallic foil against the rare earth elements was also evaluated.Our results showed that Ce and Nd in the rare earth elements and Fe in the clad material interdiffused and reacted to form intermetallic species according to the parabolic rate law,describing the migration of the rare earth element.The diffusion of Fe limited the reaction progress such that the entire process was governed by the cubic rate law.Rare earth materials could be used as a surrogate for high burnup metallic fuels,and the performance of the barrier material was demonstrated to be effective.     

Structure and Properties of Explosive Clad HSLA Steel with Titanium

The present work pertains to the study of microstructure and mechanical properties of explosively clad high strength low alloy steel with commercially pure titanium. The clad interface was characterized by metallography, hardness, shear bond strength and bend tests. The present study revealed that the clad interface was wavy in nature. Shear bond strength of clad interface was in between substrate and clad material. The three point bend tests were conducted on clad joint in such a way that cladding layer was subjected to tension and compression which have not shown any cracks at the interface. The mechanism and reasons for the observed behaviour have been discussed correlating microstructure, mechanical properties, fracture features and diffusion across the interface.     

Alloying-Element Loss During High-Temperature Processing of a Nickel-Base Superalloy

The effect of exposure at temperatures commonly used for wrought processing/heat treatment of nickel-base superalloys on the loss of alloying elements at the free surface has been determined. For this purpose, LSHR superalloy samples were exposed at 1408 K (1135 °C) for 0.25 to 4 hours in a vacuum or air furnace. Samples heat treated in the air furnace were either bare or enclosed in quartz capsules that had been evacuated or backfilled with argon. Following heat treatment, the alloy composition as a function of depth below the surface was determined by wavelength dispersive spectroscopy. Samples that had been heat treated in the vacuum furnace exhibited significant depletion of only chromium, a behavior explained on the basis of its high activity in nickel solid solution and corresponding rapid rate of evaporation. By contrast, samples heat treated in air exhibited an irregular scale at the surface and an underlying grain-coarsened, gamma-prime-depleted metal layer lean in aluminum, titanium, and chromium. A yet different behavior characterized primarily by aluminum loss at the surface was noted for samples that had been heat treated in evacuated or argon-backfilled capsules. These observations were interpreted in the context of a reaction between the quartz capsule and the aluminum evaporant.     

TC4合金基体上激光熔敷钛、铝、二氧化硅碳粉末的显微组织

Laser cladding experiment of Ti + Al + SiO2 + C was carried out on Ti6Al4V alloy substrate, thenthe microstructure of the clad layer was analyzed with SEM and its Anti - oxidation function was discussed.Analyses microstructure show that the clad coating can be divided into three zones along the depth direction:clad, binding and heat - affected zones. Ti5Si3 in the clad zone exists in the form of fine dendrites, TiAl matrix filling among Ti5Si3 dendrites plays a role of connecting the Ti5Si3 with the TiAl3 and transferring load,so the clad coating has been strengthened obviously.     

Microstructure of laser clad Ti ＋ Al ＋ SiO2 ＋ C powders on Ti6Al4V alloy

Laser cladding experiment of Ti ＋ Al ＋ SiO2 ＋ C was carried out on Ti6Al4V alloy substrate, then the micmstructure of the clad layer was analyzed with SEM and its Anti - oxidation function was discussed. Analyses microstructure show that the clad coating can be divided into three zones along the depth direction： clad, binding and heat -affected zones. Ti5Si3 in the clad zone exists in the form of fine dendrites, TiAI matrix filling among Ti5Si3 dendrites plays a role of connecting the Ti5Si3 with the TiAl3 and transferring load, so the clad coating has been strengthened obviously.     

Modeling of Heat Transfer and Fluid Flow in the Laser Multilayered Cladding Process

The current work examines the heat-and-mass transfer process in the laser multilayered cladding of H13 tool steel powder by numerical modeling and experimental validation. A multiphase transient model is developed to investigate the evolution of the temperature field and flow velocity of the liquid phase in the molten pool. The solid region of the substrate and solidified clad, the liquid region of the melted clad material, and the gas region of the surrounding air are included. In this model, a level-set method is used to track the free surface motion of the molten pool with the powder material feeding and scanning of the laser beam. An enthalpy–porosity approach is applied to deal with the solidification and melting that occurs in the cladding process. Moreover, the laser heat input and heat losses from the forced convection and heat radiation that occurs on the top surface of the deposited layer are incorporated into the source term of the governing equations. The effects of the laser power, scanning speed, and powder-feed rate on the dilution and height of the multilayered clad are investigated based on the numerical model and experimental measurements. The results show that an increase of the laser power and powder feed rate, or a reduction of the scanning speed, can increase the clad height and directly influence the remelted depth of each layer of deposition. The numerical results have a qualitative agreement with the experimental measurements.     

Microstructure and wear properties

The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10:1:1 were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO₂ laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved wear resistance is attributed to the fine distribution of metastable M₆C carbides.     

T10钢表面FeMoCoNiCrTix高熵合金熔覆层组织及性能

采用激光熔覆技术在T10A钢表面制备了FeMoCoNiCrTi_x（x分别为0.25,0.50,0.75,1.00）高熵合金熔覆层,分析了试样熔覆层及基体界面处的相结构及组织,并利用显微硬度计测试了试样处理前后的截面硬度变化。研究表明,经过激光熔覆在T10A钢表面得到的高熵合金层主要由NiCrFe、NiCrCoMo 2种固溶体为主,其结构分别为BCC结构和FCC结构,熔覆层的组织以柱状枝晶为主,界面处出现等轴晶;随着Ti含量增多,熔覆层由固溶强化变为固溶体与硬质相混合强化,熔覆层的HV硬度达到了792,热影响区的HV硬度达到了620,均高于基体硬度。同时耐磨损性能有了明显提高,磨损方式由粘着磨损逐渐变为磨粒磨损。      

Effect of Process Parameters on Clad Quality of Duplex Stainless Steel Using GMAW Process

In recent years, weld cladding are being applied in numerous industries as cost effective engineering solution to use a surface protection layer to protect carbon steel against corrosion attack. The desirable characteristics of cladding alloy are reasonable strength, weldability, resistance to general and localized corrosion attack. The duplex stainless steel having all the desirable characteristic is the candidate material for cladding. However, duplex weld metals have not been studied in detail as duplex stainless steels. Consequently, the properties of duplex weld metals are less well known and only partially understood. In the present study, the properties of duplex weld deposits of the 22 % Cr, 10 % Ni, 3 % Mo, and 0.12 % N type using GMAW process have been investigated. In particular, the influence of welding heat input and shielding gas composition in GMAW process on weld deposit microstructure, impact toughness and resistance to pitting corrosion have been studied. It is observed that concentration of nitrogen of weld deposits influenced by both heat input and shielding gas composition exerted significant effect on microstructure, low temperature toughness and resistance to pitting corrosion.     

A thermal model of laser cladding by powder injection

A two-dimensional (2-D) finite element model is presented for laser cladding by powder injection. The model simulates the quasi-steady temperature field for the longitudinal section of a clad track. It takes into account the melting of the powder in the liquid pool and the liquid/ gas free surface shape and position, which must conform to the thermal field in order to obtain a self-consistent solution. The results for an idealized problem, where there is almost no melting of the substrate material, demonstrate the linear relationship between the laser power, the processing velocity, and the thickness of the deposited layer. The calculated clad heights agreed well with the experimental values for the conditions where a cobalt-based hard-facing alloy is clad onto mild steel with a linearly focused laser source. Formerly Postdoctoral Fellow, Ecole Polytechnique Fédérale de Lausanne     

轧制温度对TA1/Q345复合板性能的影响

相对于爆炸复合法和爆炸轧制复合法而言,采用真空-轧制生产钛钢复合板的方法更加适应大规模生产需要.本实验将TA1钛材置于两块Q345钢材中间组成组合坯,组合坯经抽真空至0.1 Pa后密封,在840~930℃下进行加热轧制,对轧制复合样进行力学性能检测,并利用扫描电镜、X射线衍射分析及显微硬度仪对组织与界面结合度进行分析.在该实验条件下,钛钢复合板剪切强度在159 MPa以上,达到了1类复合板标准要求,870℃轧制复合板性能较优.900和930℃轧制时,钛发生相变,同时在界面处生成了较多的金属问化合物,钛和钢的变形抗力相差过大和变形不协调导致界面附近的内应力变大,这些因素都降低了界面的剪切强度.840℃轧制后剪切强度低的原因是由于温度过低影响了界面附近元素的扩散.      

Effect of Yttrium on Microstructure and Hot Corrosion Preformance of Laser Clad Co-Based Alloy

The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re-sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re-sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob-tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compactscale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusionof alloying elements.     

Microstructure and wear properties of laser clad Fe−Cr−Mn−C alloys

The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10∶1∶1 were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO₂ laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved wear resistance is attributed to the fine distribution of metastable M₆C carbides.     

Ti35合金焊接接头在高温硝酸中的腐蚀性能研究

以沸腾的核乏燃料后处理模拟料液及空白硝酸溶液为腐蚀液,研究了Ti35合金焊接接头的耐腐蚀性能。在模拟料液中对Ti35合金熔敷金属及焊接热模拟样进行全浸腐蚀实验,间接评价了焊接接头熔区及热影响区的耐腐蚀性能。结果表明:Ti35合金焊接接头在沸腾空白硝酸溶液及模拟料液中均具有良好的均匀腐蚀性能,焊缝熔区及热影响区的腐蚀速率大于焊接接头的腐蚀速率,焊接接头的腐蚀对焊接应力的敏感性不高;在沸腾空白硝酸介质中,硝酸浓度对焊接接头的耐蚀性能有较大的影响,随硝酸浓度的提高,焊接接头的耐蚀性能有所下降;硝酸溶液中氧化性金属阳离子对Ti35合金的焊接接头具有缓蚀作用。