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defence Technology（防务技术） 2015年第3期11卷 197-208页

作者： Ch.VENKATA RAO G.MADHUSUDHAN REDDY K.SRINIVASA RAO Department of metallurgical Engineering Andhra University defence metallurgical research laboratory

To overcome the problems of fusion welding of aluminium alloys, the friction stir welding(FSW) is recognized as an alternative joining method to improve the mechanical and corrosion properties. Tool profile is one of the important variables which affect the performance of the FS weld. In the present work, the effect of tool profile on the weld nugget microstructure and pitting corrosion of AA2219 aluminium-copper alloy was studied. FSW of AA2219 alloy was carried out using five profiles, namely conical, square, triangle, pentagon and hexagon. The temperature measurements were made in the region adjacent to the rotating pin. It was observed that the peak temperature is more in hexagonal tool pin compared to the welds produced with other tool pin profiles. It is observed that the extensive deformation experienced at the nugget zone and the evolved microstructure strongly influences the hardness and corrosion properties of the joint during FSW. It was found that the microstructure changes like grain size, misorientation and precipitate dissolution during FSW influence the hardness and corrosion behaviour. Pitting corrosion resistance of friction stir welds of AA2219 was found to be better for hexagon profile tool compared to other profiles, which was attributed to material flow and strengthening precipitate morphology in nugget zone. Higher amount of heat generation in FS welds made with hexagonal profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone.

关键词： Al-Cu合金搅拌摩擦焊微观结构焊缝区刀具腐蚀行为焊接接头性能耐腐蚀性能

Microstructure and corrosion behaviour of gas tungsten arc welds of maraging steel

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defence Technology（防务技术） 2015年第1期11卷 48-55页

作者： G.MADHUSUDHAN REDDY K.SRINIVASA RAO defence metallurgical research laboratory Department of metallurgical Engineering Andhra University

Superior properties of maraging steels make them suitable for the fabrication of components used for military applications like missile covering, rocket motor casing and ship hulls. Welding is the main process for fabrication of these components, while the maraging steels can be fusion welded using gas tungsten arc welding(GTAW) process. All these fabricated components require longer storage life and a major problem in welds is susceptible to stress corrosion cracking(SCC). The present study is aimed at studying the SCC behaviour of MDN 250(18% Ni) steel and its welds with respect to microstructural changes. In the present study, 5.2 mm thick sheets made of MDN 250 steel in the solution annealed condition was welded using GTAW process. Post-weld heat treatments of direct ageing(480 C for 3 h), solutionizing(815 C for 1 h) followed by ageing and homogenizing(1150 C for 1 h) followed by ageing were carried out. A mixture of martensite and austenite was observed in the microstructure of the fusion zone of solutionized and direct aged welds and only martensite in as-welded condition. Homogenization and ageing treatment have eliminated reverted austenite and elemental segregation. Homogenized welds also exhibited a marginal improvement in the corrosion resistance compared to those in the as-welded, solutionized and aged condition. Constant load SCC test data clearly revealed that the failure time of homogenized weld is much longer compared to other post weld treatments, and the homogenization treatment is recommended to improve the SCC life of GTA welds of MDN 250 Maraging steel.

关键词： 18% Ni maraging steel Gas tungsten arc welding Post weld heat treatment Solutionising Ageing treatment Pitting corrosion Stress corrosioncracking (SCC)

Microstructure and pitting corrosion of shielded metal arc welded high nitrogen stainless steel

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defence Technology（防务技术） 2015年第3期11卷 237-243页

作者： RAFFI MOHAMMED G.MADHUSUDHAN REDDY K.SRINIVASA RAO Department of metallurgical Engineering Andhra University defence metallurgical research laboratory

The present work is aimed at studying the microstructure and pitting corrosion behaviour of shielded metal arc welded high nitrogen steel made of Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microscopic studies were carried out using optical microscopy(OM) and field emission scanning electron microscopy(FESEM). Energy back scattered diffraction(EBSD) method was used to determine the phase analysis, grain size and orientation image mapping. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance in aerated 3.5% NaCl environment using a GillAC electrochemical system. The investigation results showed that the selected Cr-Mn-N type electrode resulted in a maximum reduction in delta-ferrite and improvement in pitting corrosion resistance of the weld zone was attributed to the coarse austenite grains owing to the reduction in active sites of the austenite/delta ferrite interface and the decrease in galvanic interaction between austenite and delta-ferrite.

关键词：耐点蚀性能高氮不锈钢焊缝金属电弧焊接研究组织屏蔽场发射扫描电子显微镜奥氏体晶粒

Microstructure and pitting corrosion resistance of AA2219 Ale Cu alloy friction stir welds e Effect of tool profile

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defence Technology（防务技术） 2015年第2期11卷 123-131页

作者： Ch VENKATA RAO G.MADHUSUDHAN REDDY K.SRINIVASA RAO Department of metallurgical Engineering Andhra University defence metallurgical research laboratory

AA2219 Ale Cu alloy is widely used in defence and aerospace applications due to required combination of high strength-to-weight ratio and *** of components used for defence always involves *** though the mechanical properties of the base metal are better,but the alloy suffers from poor mechanical and corrosion properties during fusion *** overcome the problems of fusion welding,friction stir welding(FSW) is recognized as an alternative solid state joining method aimed to improve the mechanical and corrosion *** profile is one of the important variables which affect the performance of the friction stir *** the present work the effect of tool profile on the microstructure and pitting corrosion of AA2219 aluminiumecopper alloy was *** backscattered diffraction results established that the grain size and orientation of weld nugget of triangle profile is finer than that of conical *** scanning calorimetric results show the evidence of precipitate dissolution during *** was found that the microstructure changes,such as grain size and its orientation precipitate dissolution during FSW influence the hardness and corrosion *** corrosion resistance of friction stir welds of AA2219 was found to be better for triangle profile tool compared to conical profile which is attributed to material flow and strengthening precipitate morphology in various *** amount of heat generation during FSW made using triangle profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone and coarsening in thermo mechanically affected zone(TMAZ) and heat affected zone(HAZ).

关键词： Al-Cu合金搅拌摩擦焊接微观结构轮廓点蚀摩擦搅拌焊接电子背散射衍射机械性能

Effect of Substrate and Annealing Temperatures on Mechanical Properties of Ti-rich NiTi Films

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Journal of Materials Science & Technology 2010年第11期26卷 961-966页

作者： A.Kumar S.K.Sharma S.Bysakh S.V.Kamat S.Mohan defence metallurgical research laboratory Department of Instrumentation Indian Institute of Science Central Glass and Ceramics research Institute

The effect of substrate and annealing temperatures on mechanical properties of Ti-rich NiTi films deposited on Si （100） substrates by DC magnetron sputtering was studied by *** films were deposited at two substrate temperatures viz.300 and 400 ℃.NiTi films deposited at 300 ℃ were annealed for 4 h at four different temperatures,i.e.300,400,500 and 600 C whereas films deposited at 400 ℃ were annealed for 4 h at three different temperatures,i.e.400,500 and 600 ℃.The elastic modulus and hardness of the films were found to be the same in the as-deposited as well as annealed conditions for both substrate *** a given substrate temperature,the hardness and elastic modulus were found to remain unchanged as long as the films were ***,both elastic modulus and hardness showed an increase with increasing annealing temperature as the films become *** results were explained on the basis of the change in microstructure of the film with change in annealing temperature.

关键词： NiTi thin film Annealing Nanoindentation

Friction stir surfacing of cast A356 aluminiumesilicon alloy with boron carbide and molybdenum disulphide powders

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defence Technology（防务技术） 2015年第2期11卷 140-146页

作者： R.SRINIVASU A.SAMBASIVA RAO G.MADHUSUDHAN REDDY K.SRINIVASA RAO Department of metallurgical Engineering Andhra University defence metallurgical research laboratory

Good castability and high strength properties of Ale Si alloys are useful in defence applications like torpedoes,manufacture of Missile bodies,and parts of automobile such as engine cylinders and *** wear resistance of the alloys is major limitation for their *** stir processing(FSP) is a recognized surfacing technique as it overcomes the problems of fusion route surface modification *** in view of the requirement of improving wear resistance of cast aluminiumesilicon alloy,friction stir processing was attempted for surface modification with boron carbide(B4C) and molybdenum disulfide(Mo S2) ***,micro compositional analysis,hardness and pin-on-disc wear testing were used for characterizing the surface composite *** study revealed breaking of coarse silicon needles and uniformly distributed carbides in the A356 alloy matrix after *** and uniformity in hardness was obtained in surface composite *** wear resistance was achieved in friction stir processed coating with carbide *** of solid lubricant Mo S2 powder was found to improve wear resistance of the base metal significantly.

关键词： A356合金二硫化钼堆焊技术硅合金钼粉末碳化硼摩擦铸铝

Microstructural observations on the terminal penetration of long rod projectile

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defence Technology（防务技术） 2017年第6期13卷 413-421页

作者： Krushna Kumbhar P.Ponguru Senthil A.K.Gogia Armour Design and Development Division Defence Metallurgical Research LaboratoryHyderabad 500058India

Present study focuses on the terminal penetration of tungsten heavy alloy(WHA) long rod penetrator impacted against armour steel at an impact velocity of 1600 m/s. The residual penetrator and armour steel target recovered after the ballistic test have been characterized using optical microscope, scanning electron microscope(SEM) and electron probe micro analyzer(EPMA). metallurgical changes in target steel and WHA remnant have been analysed. Large shear stresses and shear localization have resulted in local failure and formation of erosion products. Severe plastic deformation acts as precursor for formation of adiabatic shear band(ASB) induced cracks in target steel. Recovered WHA penetrator remnant also exhibits severe plastic deformation forming localized shear bands, ASB induced cracks and shock induced cracks.

关键词： Long rod projectile Terminal penetration Shear localization Adiabatic shear band Tungsten heavy alloy Armour steel

Consequence of reinforced SiC particles and post process artificial ageing on microstructure and mechanical properties of friction stir processed AA7075

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defence Technology（防务技术） 2020年第5期16卷 1039-1050页

作者： H.A.Deore A.Bhardwaj A.G.Rao J.Mishra V.D.Hiwarkar Department of metallurgical and Materials Engineering Defence Institute of Advanced TechnologyPune411025India Naval Material research laboratory(NMRL) Defence Research Development OrganizationMinistry of DefenceAmbarnath414006India

Friction stir processing and post process artificial ageing was successfully carried out on AA7075 with and without reinforcement of SiC particles producing defect free processed zone with uniform distribution of filler *** of SiC particle reinforcement and artificial ageing times on the microstructural modifications was characterized using optical and electron microscopy,electron backscattered diffraction and X-Ray ***,impact and wear tests were carried out to investigate mechanical behaviour before and after *** of SiC particles during FSP and subsequent age hardening treatment brought about nearly twofold increase in hardness and impact toughness values by the combined effect of grain refinement,Zener pinning,dispersion strengthening and precipitation *** improvement in wear resistance in terms of wear loss was also observed after processing compared to the reference material *** surface of post FSP age hardened AA7075 alloy exhibited features of ductile fracture during Charpy impact test.

关键词： Friction stir processing EBSD Impact toughness Post process age hardening Zener pinning

Optimization of process parameters of aluminum alloy AA 2014-T6 friction stir welds by response surface methodology

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defence Technology（防务技术） 2015年第3期11卷 209-219页

作者： Ramanjaneyulu KADAGANCHI Madhusudhan Reddy GANKIDI Hina GOKHALE Mahatma Gandhi Institute of Technology defence metallurgical research laboratory

The heat treatable aluminum-copper alloy AA2014 finds wide application in the aerospace and defence industry due to its high strength-toweight ratio and good ductility. Friction stir welding(FSW) process, an emerging solid state joining process, is suitable for joining this alloy compared to fusion welding processes. This work presents the formulation of a mathematical model with process parameters and tool geometry to predict the responses of friction stir welds of AA 2014-T6 aluminum alloy, viz yield strength, tensile strength and ductility. The most influential process parameters considered are spindle speed, welding speed, tilt angle and tool pin profile. A four-factor, five-level central composite design was used and a response surface methodology(RSM) was employed to develop the regression models to predict the *** mechanical properties, such as yield strength(YS), ultimate tensile strength(UTS) and percentage elongation(%El), are considered as responses. Method of analysis of variance was used to determine the important process parameters that affect the responses. Validation trials were carried out to validate these results. These results indicate that the friction stir welds of AA 2014-T6 aluminum alloy welded with hexagonal tool pin profile have the highest tensile strength and elongation, whereas the joints fabricated with conical tool pin profile have the lowest tensile strength and elongation.

关键词：焊接工艺参数搅拌摩擦焊铝合金焊接响应面分析法抗拉强度优化焊接接头屈服强度

Neural network modeling to evaluate the dynamic flow stress of high strength armor steels under high strain rate compression

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defence Technology（防务技术） 2014年第4期10卷 334-342页

作者： Ravindranadh BOBBILI V.MADHU A.K.GOGIA defence metallurgical research laboratory Hyderabad 500058 India

An artificial neural network(ANN) constitutive model is developed for high strength armor steel tempered at 500 C, 600 C and 650 C based on high strain rate data generated from split Hopkinson pressure bar(SHPB) experiments. A new neural network configuration consisting of both training and validation is effectively employed to predict flow stress. Tempering temperature, strain rate and strain are considered as inputs, whereas flow stress is taken as output of the neural network. A comparative study on Johnsone Cook(Je C) model and neural network model is performed. It was observed that the developed neural network model could predict flow stress under various strain rates and tempering temperatures. The experimental stressestrain data obtained from high strain rate compression tests using SHPB, over a range of tempering temperatures(500e650 C), strains(0.05e0.2) and strain rates(1000e5500/s) are employed to formulate Je C model to predict the high strain rate deformation behavior of high strength armor steels. The J-C model and the back-propagation ANN model were developed to predict the high strain rate deformation behavior of high strength armor steel and their predictability is evaluated in terms of correlation coefficient(R) and average absolute relative error(AARE). R and AARE for the Je C model are found to be 0.7461 and 27.624%, respectively, while R and AARE for the ANN model are 0.9995 and 2.58%, respectively. It was observed that the predictions by ANN model are in consistence with the experimental data for all tempering temperatures.

关键词：人工神经网络模型高应变率高强度装甲钢流变应力可预测性压缩评估