Application of response surface methodology to maximize tensile strength and minimize interface hardness of friction welded dissimilar joints of austenitic stainless steel and copper alloy

An attempt was made to optimize friction welding parameters to attain a minimum hardness at the interface and a maximum tensile strength of the dissimilar joints of AISI 304 austenitic stainless steel （ASS） and copper （Cu） alloy using response surface methodology （RSM）. Three-factor, five-level central composite design matrix was used to specify experimental conditions. Twenty joints were fabricated using ASS and Cu alloy. Tensile strength and interface hardness were measured experimentally. Analysis of variance （ANOVA） method was used to find out significant main and interaction parameters and empirical relationships were developed using regression analysis. The friction welding parameters were optimized by constructing response graphs and contour plots using design expert software. The developed empirical relationships can be effectively used to predict tensile strength and interface hardness of friction welded ASS-Cu joints at 95% confidence level. The developed contour plots can be used to attain required level of optimum conditions to join ASS-Cu alloy by friction welding process.

A Hybrid Low Temperature Surface Alloying Process for Austenitic Stainless Steels

This paper describes a novel, hybrid process developed to engineer the surfaces of austenitic stainless steels at temperatures below 450°C for the improvement in wear and corrosion resistance. The process is carried out in the plasma of a glow discharge containing both nitrogen and carbon reactive species, and facilitates the incorporation of both nitrogen and carbon into the austenite surface to form a dual-layer structure comprising a nitrogen-rich layer on top of a carbon-rich layer. Both layers can be precipitation-free at sufficiently low processing temperatures, and contain nitrogen and carbon respectively in supersaturated fee austenite solid solutions. The resultant hybrid structure offers several advantages over the conventional low temperature nitriding and the newly developed carburizing processes in terms of mechanical and chemical properties, including higher surface hardness, a hardness gradient from the surface towards the layer-core interface, uniform layer thickness, and much enhanced corrosion resistance. This paper discusses the main features of this hybrid process and the various structural and properties characteristics of the resultant engineered surfaces.

Laser Surface Modification of Lean-alloyed Austenitic Stainless Steel for Corrosion Resistance

In order to reduce the cost of the austenitic stainless steels(ASSs),the expensive austenite former(nickel) is often substituted by manganese.However,manganese is generally seen to have a detrimental effect on the corrosion resistance.In the present study,the feasibility of laser surface modification of a lean-alloyed ASS(FeCrMn) for enhancing pitting corrosion resistance was investigated.Laser surface modification of FeCrMn was successfully achieved by a 2.3 kW high power diode laser(HPDL).Cyclic polarization tests for FeCrMn after laser surface modification in 3.5% NaCl solution at 25 ℃ were performed by using a potentiostat.The pitting resistance of the laser-modified specimens was found to be significantly improved as reflected by the noble shift in pitting potential.This could be attributed to redistribution of manganese sulphide leading to a more homogenous and refined microstructure.Pitting corrosion resistance of the laser-treated FeCrMn followed by subsequent citric acid passivation was found to be further improved as reflected by the noble shift in pitting potential to 0.18 V.

Cavitation erosion behavior of WC coatings on CrNiMo stainless steel by laser alloying

The WC powder was precoated on the surface of CrNiMo stainless steel and then made into an alloying layer by using the laser alloying technique. Phases in the layers were investigated by X-ray diffraction （XRD） analysis and surface morphologies after cavitation erosion were observed with the help of scanning electron microscopy （SEM）. The cavitation erosion behavior of the CrNiMo stainless steel and WC laser alloying layer in distilled water was tested with the help of ultrasonic vibration cavitation erosion equipment. The results showed that the thickness of the laser alloying layer was about 0.13 mm. The layer had a dense microstructure, metallurgically bonded to the substrate, and no crack had been found. The cavitation erosion mass loss rate of the laser alloying layer was only 2/5 that of the CrNiMo stainless steel. The layer had better cavitation resistance properties because of its metallurgical combination and the strengthening effects of the precipitate phases.

Prediction and optimization of friction welding parameters for joining aluminium alloy and stainless steel

Friction welding （FW） is a process of solid state joining which is used extensively in recent years due to its advantages such as low heat input,production efficiency,ease of manufacture and environment friendliness.Friction welding can be used to join different types of ferrous metals and non-ferrous metals that cannot be welded by traditional fusion welding processes.The process parameters such as friction pressure,forging force,friction time and forging time play the major roles in determining the strength of the joints.In this investigation an attempt was made to develop an empirical relationship to predict the tensile strength of friction welded AA 6082 aluminium alloy and AISI 304 austenitic stainless steels joints,incorporating above said parameters.Response surface methodology （RSM） was applied to optimizing the friction welding process parameters to attain the maximum tensile strength of the joint.

Effects of C,N-Codoped on the Corrosion Resistance of TiO_2 Films Prepared by Plasma Surface Alloying and Thermal Oxidation Duplex Process

C,N-codoped TiO 2 films have been deposited onto stainless steel substrates using plasma surface alloying and thermal oxidation duplex process.Composition analysis shows that the films shield the substrates entirely.The TiO 2 films are anatase in structure as characterized by X-ray diffraction.The electrochemical measurements show that the equilibrium corrosion potential positively shifts from-0.275 eV for bare stainless steel to-0.267 eV for C,N-codoped TiO 2 coated stainless steel,and the corrosion current density decreases from 1.3×10-5 A/cm2 to 4.1×10-6 A/cm2.The corrosion resistance obtained by electrochemistry noise also reveals that the C,N-codoped TiO 2 films provide good protection for stainless steel against corrosion in stimulated body fluid.The above results indicate that C,N-codoped TiO 2 films deposited by plasma surface alloying and thermal oxidation duplex process are effective in protecting stainless steel from corrosion.

Microstructure and Wear Resistance of N-Doped TiO_2 Coatings Grown on Stainless Steel by Plasma Surface Alloying Technology

N doped TiO2 （N-TiO2） coatings were obtained by oxidation of titanium nitride coatings, which were pre pared by the plasma surface alloying technique on stainless steel （SS）. The microstructure of N-TiO2 coatings was characterized by X-ray diffraction （XRD）, glow discharge optical emission spectrometry （GDOES）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）, respectively. Ball-on-disc sliding wear was applied to test and compare the tribological behaviors of the coatings and substrate. XRD patterns showed that anatase type TiO2 existed in the coatings after oxidation. GDOES showed that the resultant coatings had a layered structure, comprising of N-TiO2 layer at the top and a diffusion-type interface. Such a hybrid coatings system showed good adhesion with the substrate. According to XPS, residual N atoms partially occupied O atom sites in the TiO2 lattice. Uniform, continuous and compact coatings were observed by SEM images of coatings after oxidation. Under a load of 7.6 N, the coefficient of friction was in the range of 0.27--0.38 for the N-TiO2/Al2O3 systems and the wear rate of the coatings was only one-fourteenth of that for untreated 316L SS. N-TiO2 coatings displayed much better wear resistance and antifrietion performance than SS substrate.

Role of Microstructural Constituents on Surface Crack Formation During Hot Rolling of Standard and Low Nickel Austenitic Stainless Steels

The effect of alloy segregation and delta （δ） ferrite contents on surface cracking of three standard （i.e. AISI 304L, AISI 310S and AISI 321） and two low nickel （i.e. LNi-1 and LNi-0.3） austenitic stainless steels （ASS） during hot roiling was investigated using optical microscopy （OM）, automatic image analyzer, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDX） and electron probe micro analyzer （EPMA）. It was observed that the amount of 6-ferrite varied among different grades and also distributed heterogeneously across the width of the steel plates. In general, low nickel ASS showed higher amount of 6-ferrite compared to the standard ASS grades. The tendency to surface cracking during hot rolling gradually increased with increasing 6-ferrite content. Interestingly, carbon and nitrogen exerted maximum effect on 6-ferrite formation. The higher carbon and nitrogen content in the steel decreased 6-ferMte content. In addition, the segregation of Cu and Mn plays significant role in low nickel ASS and Ni-Cr in case of standard ASS has profound effect on surface cracking of the steel plates. A possible cause of surface crack formation/origination in steel plates during hot rolling was discussed.

汽车用不锈钢表面激光熔覆CoCrNi中熵合金熔覆层微观组织及耐蚀性研究

为提升车用304不锈钢的表面硬度及耐蚀性,采用激光熔覆技术在304不锈钢表面制备了CoCrNi中熵合金熔覆层,并研究了熔覆层的相组成、元素分布及耐蚀性能。结果表明,CoCrNi中熵合金熔覆层与基体形成了良好的冶金结合,无裂纹、气孔等缺陷;熔覆层由单一FCC相组成,组织为枝晶、枝晶间结构,各元素在熔覆层中均匀分布,无明显偏析现象,Cr元素的均匀分布对提升涂层耐蚀性具有积极作用;CoCrNi中熵合金熔覆层的极化电阻(101.65 kΩ)高于304基体的极化电阻(90.56 kΩ),耐蚀性明显高于304基体。

铜基合金模具材料的研究

介绍了一种可成功地用于不锈钢器皿和08F低碳钢制品拉伸成形的新型铜基合金模具材料。试验结果证实，该材料能彻底克服产品表面极易产生的划痕、划伤等表面缺陷。

双层辉光法制备含银抗菌不锈钢层工艺

为了研究双层辉光法制备含银抗菌不锈钢层，通过抗菌试验、盐干湿循环腐蚀试验、SEM、XPS等手段，研究了扩散工艺参数与抗菌性能、耐蚀性能之间的关系。结果表明，双层辉光法制备含银抗菌不锈钢层的可行工艺参数为：电压1．2kV，气流量为20～40ml／min，时间为3h；含银抗菌不锈钢的杀菌率可达到100％，耐蚀性能没有降低；银在基体中呈弥散状态分布，其价态为一价。

表面自纳米化对钛合金与不锈钢的扩散焊接的影响

用恒温恒压扩散焊接法实现了表面纳米化后的TA17近α型钛合金与0Cr18Ni9Ti不锈钢的连接。焊接材料用气动喷丸方式进行表面自纳米化。利用液压万能试验机测试了接头拉伸强度,并对焊接接头及断口形貌和组织进行了扫描电镜观察及能谱分析。结果表明:接头界面附近出现了不同的层,在不同温度下的焊接接头组织及分布大致相同;与未对材料进行表面自纳米化处理相比,材料经表面自纳米化处理后,加快了被焊偶件的接触进程,提高了原子的扩散速率和焊接接头的强度,并缩短了焊接时间。

316L不锈钢强流脉冲电子束表面钛合金化及其耐蚀性

利用强流脉冲电子束对不锈钢表面进行了快速钛合金化。将精细钛粉预涂在基体表面后采用强流脉冲电子束对其进行后处理。在电子束对表面的快速加热熔化、混合及增强扩散效应的作用下,部分钛熔入基体表层形成一层富钛层。由于钛的添加有利于形成α相,合金层由α相和γ相混合组成。在模拟体液中的动态极化测试表明,316L医用不锈钢经强流脉冲电子束表面钛合金化后,其在模拟体液中的耐腐蚀性能获得了显著的提高。

不锈钢表面激光合金化Cr-CrB_2层的腐蚀性研究

为了提高SUS 304不锈钢表面的耐磨损、耐腐蚀性能,采用激光表面合金化的方法制备了Cr-CrB2层,并进行了理论分析和实验验证,取得了合金化层的组织和物相以及电化学腐蚀性数据。结果表明,合金化层组织致密、晶粒细小,与基体形成冶金结合,合金化层由奥氏体、马氏体、铁铬固溶体、碳化物和铬硼化合物组成;合金化层的耐蚀性得到提高,腐蚀速率降低,合金化层的极化曲线具有较长的活化-钝化区间;不锈钢基体发生严重的晶界腐蚀和点蚀,晶界腐蚀以孪晶晶界腐蚀为主,合金化层表面发生晶粒间的晶界腐蚀,伴有晶粒和晶界处的点蚀现象,点蚀坑明显小于基体表面的点蚀坑。这一结果对提高SUS 304不锈钢表面的耐磨损、耐腐蚀性是有帮助的。

不锈钢表面修饰纳米合金膜电极的电催化活性研究

以不锈钢(SS)作基底,自行研制不锈钢载纳米表面合金电催化材料(Surface alloy/SS),并运用循环伏安法(CV)和扫描电镜(SEM)等技术对该催化剂进行结构和性能表征.SEM研究表明,所研制的Surface alloy/SS电催化剂是一种由粒度主要约为100nm的颗粒合金组成的薄膜.循环伏安研究表明,所研制的Surface alloy/SS电催化剂在常温常压下对顺丁烯二酸的加氢还原表现出很高的电催化活性.顺丁烯二酸的起始还原电位为-0.4V,与通常用的阴极铅材料相比,正移约200mV.

表面纳米化钛合金与不锈钢脉冲加压扩散连接

采用高能喷丸(HESP)对TA17钛合金和0Cr18Ni9Ti不锈钢棒材的端面进行了表面自纳米化(SSNC)处理,在端面获得了一定厚度的纳米晶组织层。将钛合金和不锈钢的纳米化处理端面对接,在Gleeble—1500D热模拟试验机上进行脉冲加压扩散连接。对接头进行了拉伸试验,并对断口和接头显微组织进行了研究分析。结果表明,接头强度高达384.0 MPa,与在相同条件下获得的常规粗晶的接头强度相比,有显著的提高。接头在拉伸时发生脆性断裂,接头剖面的显微硬度随显微组织而变化。

AZ31镁合金表面气相沉积不锈钢薄膜的实验研究

利用真空蒸发镀膜技术在镁合金表面沉积不锈钢薄膜是提高镁合金防腐性能的新尝试。本研究利用该技术在AZ31上成功制备了不锈钢薄膜。通过在5%NaCl溶液中的浸入实验和极化实验考察了腐蚀性能,发现镀膜后耐蚀性显著降低。另外,镀膜后的显微硬度也未有明显提高。利用AFM,SEM,EDX等分析手段对薄膜进行了观察和检测,发现耐蚀性变差的原因主要是薄膜表面存在贯穿性的微米级孔洞和Cr元素分布不均匀造成的。

医用金属材料腐蚀疲劳性能研究进展

结合文献和课题组的研究,对医用金属材料腐蚀疲劳性能的研究进展进行了总结,分别从腐蚀疲劳的危害性、分类、设计、控制等几个方面进行了阐述。腐蚀疲劳失效首先发生于材料表面,医用材料-生理环境的界面对于植入器械手术成功与否有着至关重要的作用,可以根据裂纹扩展速度曲线特征,将腐蚀疲劳分为三类。医用金属材料的腐蚀疲劳性能研究应考量其服役环境进行设计,可以通过表面处理、合金化等方法改善医用金属材料的腐蚀疲劳性能。医用金属材料腐蚀疲劳性能研究的一些基础问题仍待解决:医用金属材料在微生物参与下的腐蚀疲劳行为及其相关机制亟待阐述;医用金属材料的微生物腐蚀疲劳研究是一个系统、长期、复杂的过程,需要合理地建立实验模型,将三维有限元与传统实验方法有机结合,进一步指导医用金属材料相关器械的设计;新的合金成分设计、新的加工制造方式所获得的新型合金生理环境下的腐蚀疲劳性能,其相关数据亟待完善,这关系到新型医用金属材料长期使用的生物安全性问题,亟需开展大量的基础研究工作。在综合评述医用金属材料腐蚀疲劳性能研究现状的基础上,对医用金属腐蚀疲劳在学科交叉研究和新材料基础研究方面的发展趋势进行了展望。

铁基合金抗冲蚀性能主要控制因素的分析

用旋转圆盘实验机对2种超弹性Fe-Mn-Si-Cr形状记忆合金、5种Cr-Ni不锈钢和1种新型高铬铸铁的抗冲蚀性能进行了研究,通过SEM和XRD以及犁削抗力和局域弹性的模拟测定,探索了硬度、犁削抗力,弹性性质和相变对抗冲蚀性能的影响．结果表明,冲蚀微观失效机制是泥沙犁削．犁削抗力W_p与局域弹性h_e是不锈钢和Fe-Mn-Si-Cr形状记忆合金抗冲蚀性能的主要控制因素。其冲蚀率R_e与局域弹性h_e值和犁削抗力W_p值之间存在着相关性较高的量化表征关系式．相变在抗冲蚀性能中的作用取决于局域弹性h_e和犁削抗力W_p的综合效应．形状记忆合金0Mn25Cr7Si6Cu抗冲蚀性能因诱发的密排六方ε马氏体具有高的局域弹性h_e而优于除高铬铸铁以外的所有其它实验材料．

1Cr11MoNiW1VNbN钢堆焊司太立合金工艺

1Cr11MoNiW1VNbN钢为马氏体不锈钢,焊接时易出现冷裂纹和再热裂纹。司太立合金为耐磨硬质合金,强度和硬度高,塑韧性差,焊接性差,因此堆焊需要选择合适的焊材焊接过渡层,制定严格的焊接和热处理工艺,避免焊接裂纹的产生,满足使用要求。选择镍基合金作为过渡层,并严格控制工艺参数,获得理想的堆焊层,验证了堆焊工艺的可行性,实现了指导工业生产的目的。