Micro Structural Investigation On Friction Stir Welded Al–4.5Cu–5TiB<Subscript>2</Subscript> Composite

Aluminium matrix composites are widely used in defence and aerospace applications. Welding them is very difficult and is an outstanding issue in a cost effective way. Friction stir welding is a solid state welding technique which is circumventing those barriers and is applied successfully to many such materials recently. In the present work, Al–4.5Cu alloy with TiB₂ reinforcement as in situ which was synthesized by stir casting method was welded by friction stir welding. Threaded pin was used as the friction stir tool profile. One of the joints was found to have tunnel defect in the stir zone due to improper material flow. The microstructural investigation through XRD and SEM revealed that the nugget zone had numerous small particles and refined fine grains which were distributed uniformly and hardness at the welded zone was found to be higher than that of the base material.     

Transformation and Deformation Texture Study in Friction Stir Processed API X80 Pipeline Steel

The nature of deformation in friction stir welding/processing (FSW/P) is complex which is further complicated when allotropic phase transformations are present. Electron backscattered diffraction (EBSD) is used as a means to reconstruct prior austenite texture and grain structure to study deformation and recrystallization in austenite and ferrite in FSW/P of high strength low alloy (HSLA) steels. Analyses show evidence of shear deformation textures such as A1* (111)[?1?12], B (1?12)[110], and ?B (?11?2)[?1?10], as well as rotated-cube recrystallization texture in the reconstructed prior austenite. Existence of rotated-cube texture as well as polygonal grain structure of the prior austenite implies that recrystallization is partially occurring in elevated temperatures. Room temperature ferrite exhibits well-defined shear deformation texture components. The observed shear deformation texture in the room temperature microstructure implies that FSW/P imposes deformation during the phase transformation. The evolution of both elevated and room temperature textures in friction stir processed API X80 steel are presented.     

Fabrications of Surface Nanocomposite by Friction Stir Processing to Improve Mechanical and Microstructural Properties of Low Carbon Steel

Friction stir processing was used to fabricate metal matrix composites on the surface of low carbon steel. In this research for making 2 mm surface MMC, the groove method was applied to fabricate TiB₂ nanocomposite via cylindrical tool made of tungsten carbide. Microstructural properties of FSPed samples were studied by optical microscopy and scanning electron microscopy. To evaluate mechanical properties, the micro hardness and tensile properties of MMC were measured. The results indicated that the surface nanocomposite produced by this method had excellent properties. The microstructure of surface MMCs became fine (ferrite grain size became about 1–2 µm) with no defect and porosity. Moreover by adding TiB₂ nanoparticles to the low carbon steel matrix alloy, mechanical properties were improved. Micro hardness can become 200HV higher than that of the base metal. The surface nanocomposite also exhibited better tensile strength when sample yield stress increased to about 28 %.     

Characterisation of Ag–Sn–Cu Dental Amalgam Powder and Its Amalgam Triturated with Nominal and Higher Pressure

Ag–Sn–Cu lathe cut particles of dental amalgam powders are mixed with mercury with an approximate 1:1 ratio. Mercury and amalgam powder mixtures are triturated at nominal pressure and at higher pressure applied intermittently, and then condensed into an acrylic mould with reasonably higher condensation pressure as well, followed by setting at room temperature for different time period. The microstructural features of the amalgam alloy powders and its amalgams of various states are studied by FESEM, X-ray elemental mapping, X-ray diffraction, differential scanning calorimetry and by hardness measurement as well. Results showed that the amalgams triturated with higher pressure have yielded finer matrix γ₁ (Ag₂Hg₃), presence of Ag-rich β₁ and finer unreacted γ (Ag₃Sn) phases with reduced porosity and higher hardness.     

Comparison of Friction Stir and Gas Tungsten Arc Weldments of Modified 12 wt.% Cr Ferritic Stainless Steel

This paper presents the comparative evaluation of microstructural features and mechanical properties of a friction stir welded (solid‐state) and gas tungsten arc welded (fusion weld) 409 M grade ferritic stainless steel joints. Optical microscopy, microhardness, transverse tensile and impact tests were performed. The coarser ferrite grains in the base material are changed to very fine grains consisting of a duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. On the other hand, grain growth was observed in the fusion zone as well as heat affected zone of the gas tungsten arc welded joint resulting in deterioration of mechanical properties.     

Friction Stir Processing for Enhancement of Wear Resistance of ZM21 Magnesium Alloy

Present work pertains to surface modification of the magnesium alloy using friction stir processing (FSP). Silicon carbide and boron carbide powders are used in the friction stir processing of the ZM21 Magnesium alloy. Coating was formed by FSP of the alloy by placing the carbide powders into the holes made on the surface. Surface coating was characterized by metallography, hardness and pin-on-disc testing. Friction stir processed coating exhibited excellent wear resistance and is attributed to grain boundary pinning and dispersion hardening caused by carbide particles. Surface composite coating with boron carbide was found to possess better wear resistance than coating made with silicon carbide. This may be attributed to formation of very hard layer coating of boron carbide reinforced composite on the surface of magnesium alloy. In the present work an attempt has also been made to compare the wear behaviour of surface composite layer on ZM21 Mg alloy with that of conventionally used engineering materials such as mild steel and austenitic stainless steel. Wear data clearly shows that wear resistance of friction stir processed composite layer is better than that of mild steel and stainless steel. This work demonstrates that friction stir processing is an effective strategy for enhancement of wear resistance of magnesium alloys.     

α″ Martensite and Amorphous Phase Transformation Mechanism in TiNbTaZr Alloy Incorporated with TiO<Subscript>2</Subscript> Particles During Friction Stir Processing

This work studied the formation of the α″ martensite and amorphous phases of TiNbTaZr alloy incorporated with TiO₂ particles during friction stir processing. Formation of the amorphous phase in the top surface mainly results from the dissolution of oxygen, rearrangement of the lattice structure, and dislocations. High-stress stemming caused by dislocations and high-stress concentrations at crystal–amorphous interfaces promote the formation of α″ martensite. Meanwhile, an α″ martensitic transformation is hindered by oxygen diffusion from TiO₂ to the matrix, thereby increasing resistance to shear.     

Strain Rate Sensitivity,Work Hardening,and Fracture Behavior of an Al-Mg TiO2 Nanocomposite Prepared by Friction Stir Processing

Annealed and wrought AA5052 aluminum alloy was subjected to friction stir processing (FSP) without and with 3 vol pct TiO₂ nanoparticles. Microstructural studies by electron backscattered diffraction and transmission electron microscopy showed the formation of an ultra-fine-grained structure with fine distribution of TiO₂ nanoparticles in the metal matrix. Nanometric Al₃Ti and MgO particles were also observed, revealing in-situ solid-state reactions between Al and Mg with TiO₂. Tensile testing at different strain rates determined that FSP decreased the strain rate sensitivity and work hardening of annealed Al-Mg alloy without and with TiO₂ nanoparticles, while opposite results were obtained for the wrought alloy. Fractographic studies exhibited that the presence of hard reinforcement particles changed the fracture mode from ductile rupture to ductile-brittle fracture. Notably, the failure mechanism was also altered from shear to tensile rupture as the strain rate increased. Consequently, the fracture surface contained hemispherical equiaxed dimples instead of parabolic ones.     

电弧增材制造HSLA钢的组织演变行为与力学性能

 电弧增材制造是成形高性能HSLA钢构件的重要新方法。为了明晰HSLA钢在电弧增材制造时的组织演变行为,研究了构件在堆积成形时的温度场、热循环、热影响区分区及其组织转变。结果表明,电弧增材制造过程中,HSLA钢堆积金属包含凝固区与热影响区,热影响区可分为粗晶区、正火区和回火区。凝固区在热循环作用下先后转变为粗晶区、正火区,最终成为回火区;同时,堆积金属中的残留铁素体晶核、夹杂物附近的高密度位错、铁素体感生形核、第二相质点钉扎晶界和连续动态再结晶共同促进组织细化,使粗大的柱状晶、块状铁素体、侧板条铁素体以及少量针状铁素体、珠光体演变为细小的等轴铁素体和珠光体,有利于提高构件强韧性并抑制力学性能各向异性。构件垂直与水平抗拉强度分别为519.6、520.8 MPa,-20 ℃冲击功分别为124.7、122.1 J。     

Sliding Wear Behavior Solid Lubricant Based Ni–Al–Bronze Surface Composite Developed by Friction Stir Processing

In this study, a nickel aluminium bronze (NAB) metal matrix composite reinforced with solid lubricants i.e. graphite and molybdenum disulphide (MoS₂) was prepared by friction stir processing. Friction stir processing (FSP) refined the grain structure as compared to the as-cast NAB. The micrographs of graphite reinforced matrix revealed fine globular α phase with some elongated morphology α phases, whereas MoS₂ reinforced surface composite mainly exhibited fine α phase particles. FSP also resulted in the distribution of solid lubricant particles in the NAB matrix. The hardness of the composites decreased with the addition of the solid lubricants in NAB matrix. SEM–EDS analysis of the reinforced NAB matrix confirmed the presence of solid lubricants. The influence of solid lubricants on the sliding wear behavior of NAB metal matrix was investigated by using the design of experimental approach. The experimental results revealed better wear resistance of the NAB–MoS₂ surface composite as compared to graphite reinforced and FSPed NAB surface. SEM–EDS analysis of worn out surfaces and wear debris were carried out for understanding the wear mechanism.     

The role of grain size and ferrite substructure in respect to mechanical properties of an HSLA steel

Several heat treatments were applied to an HSLA steel of type StE 460 (German standard) to produce four ferrite substructures of different strength and at least two different grain sizes respectively. Whereas the ferrite substructure had a strong influence on yield strength the effect of grain size was negligible though probably to some extent masked by different pearlite volume fractions. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbonitride particles and their mutual interaction. Increasing both grain size and pearlite volume fraction leads to a remarkable shift of transition temperature T_27J which was further enhanced by increasing ferrite strength.     

Ti-Y2O3 Composites with Nanocrystalline and Microcrystalline Matrix

Mechanical milling of a Ti-2 pct Y₂O₃ powders mixture led to the synthesizing of a composite powder with a nanocrystalline Ti matrix having a mean crystallite size of 19 nm. Both the nanocomposite powder prepared through milling and the initial mixture of powders were consolidated by hot pressing under the pressure of 7.7 GPa at the temperature of 1273 K (1000 °C). The transmission electron microscopy (TEM) investigations of the bulk sample produced from milled powder revealed that Y₂O₃ equiaxial particles of less than 30 nm in size are distributed uniformly in the Ti matrix with a grain size in the wide range from 50 nm to 200 nm. The microhardness of the produced nanocrystalline material is 655 HV0.2, and it significantly exceeds the hardness of the microcrystalline material (the consolidated initial mixture of powders), which is equal to 273 HV0.2. This finding confirms that reducing the grain size to the nanometric level can have a beneficial influence on the hardness of titanium alloys. Dispersion hardening also contributes to the hardness increase.     

Microstructure,Tensile and Impact Toughness Properties of Friction Stir Welded Mild Steel

 Microstructure, tensile and impact toughness properties and fracture location of friction stir welded AISI 1018 mild steel are revealed in this paper. The 5 mm thick AISI 1018 mild steel plates were friction stir welded with tool rotational speed of 1000 rpm and welding speed of 50 mm/min with tungsten base alloy tool. Tensile strength of stir zone is higher (8%) when compared to the base metal. This may be due to the formation of finer grains in the weld nugget region under the stirring action of the rotating tool. The ductility and impact toughness of the joints are decreased compared to the base metal and this is due to the inclusion of tungsten particles in the weld region.     

搅拌摩擦加工IF钢的组织性能

对3 mm厚的DC04冷轧IF钢板进行搅拌摩擦加工,研究加工区域的微观组织与力学性能.在旋转速度为950 r·min-1,加工速度为60 mm·min-1时,采用加工后强制冷却技术可获得光滑平整且没有缺陷的加工表面.搅拌摩擦加工后组织显著细化,加工中心的平均显微硬度约为HV 135.6,是母材硬度的1.4倍,表面细晶层硬度最高可达到HV 312.8,细晶层和过渡层的抗拉强度分别比母材的抗拉强度提高50.9%和47.6%,加工前后试样的拉伸断口均呈微孔聚合韧性断裂特征.细晶强化对材料抗拉强度的提高起主要作用.      

Investigation on Metallurgical Structure and Mechanical Properties of Dissimilar Al 2024/Cu FSW T-joints

In this research, T-joining of AA2024-T4 and commercially pure copper were performed successfully using friction stir welding. Effect of welding parameters on metallurgical and mechanical characteristics of the joints was studied. For this purpose, tensile strength, microhardness, and macro- and microstructures of the joints were investigated. Also, the fracture surfaces were examined using XRD and SEM. The best results were obtained for the 1130 rpm rotation speed (ω) and 12 mm/min travel speed (v), with the UTS of 156 MPa (~70% of Cu strength). The microhardness test showed that TMAZ and base metal of Al side had the maximum hardness amounts (148 and 155 HV, respectively). Generally, increase in the ω²/v ratio caused the nugget zone and HAZ grain size to increase. The results revealed the formation of Al₂Cu and Al₄Cu₉ intermetallic compounds in the border zone of the joints. The fractography results showed the occurrence of cleavage fracture in all the samples.     

Mechanical and Electrochemical Behavior of a High Strength Low Alloy Steel of Different Grain Sizes

Various heat treatments applied to a fine-grained high strength low alloy (HSLA) steel resulted in producing different grain sizes. Optical and scanning electron microstructures of the different alloy states exhibited varying ferrite grains which have increased with the increase of annealing time and decrease of cooling rates. TEM structures of the as-received HSLA steel displayed characteristics microstructural features, distribution, and morphology of microalloy precipitates. Hardness and tensile strength values have decreased with the increase of grain sizes. Potentiodynamic electrochemical polarization of the different alloy states in 3.5 wt pct NaCl solution showed typical active metal/alloy behavior. Tensile specimens of the as-received and heat-treated alloy cathodically charged with hydrogen, followed by tensile testing, did not indicate any noticeable loss of ductility. FESEM fractographs of hydrogen-charged samples showed a few chain of voids in the presence of cup and cone ductile fracture features in tensile-tested samples without hydrogen charging as well.     

Producing of AA5083/ZrO2 Nanocomposite by Friction Stir Processing (FSP)

In this study, friction stir processing (FSP) was used to produce AA5083/ZrO₂ nanocomposite layer. Optical microscopy and SEM were used to probe the microstructures formed in the composite layer. In addition, the mechanical properties of each sample are characterized using both tensile and hardness tests. Results showed that FSP is an effective process to fabricate AA5083/ZrO₂ nanocomposite layer with uniform distribution of ZrO₂ particles, good interfacial integrity, and significant grain refinement. On processing, in the proper combination of process parameters, the metal matrix composite layer was observed to have increased tensile and hardness properties.     

Investigation of a discus-milling process using a powder mixture of Al and TiO2

In this study, a powder mixture of Al and TiO₂ was employed to investigate the milling process in a discus mill. In this first report on this novel mechanical mill, several variables, including the milling time and powder charge and their effects on the microstructural evolution of powder particles, are monitored and studied. The study reveals that the dominant parameters of the milling process are the milling time and the starting powder charge, similar to the other high-energy ball-milling processes. The longer the milling time and the smaller the starting powder charge, the more homogeneous the mixing and the finer the microstructure of the powder particles. The reaction between Al and TiO₂ was not observed with a milling period as long as 6 hours, for the present materials. However, the reaction between Al and TiO₂, during the subsequent heat treatment, is influenced by the milling condition. The powders with the longer milling times and finer mixing microstructures also form a finer microstructure, after the reaction between Al and TiO₂ during heat treatment. The methods for achieving an optimal milling efficiency for the Al-TiO₂ system are discussed.     

Functionally Graded Al Alloy Matrix <Emphasis Type="Italic">In-Situ</Emphasis> Composites

In the present work, functionally graded (FG) aluminum alloy matrix in-situ composites (FG-AMCs) with TiB₂ and TiC reinforcements were synthesized using the horizontal centrifugal casting process. A commercial Al-Si alloy (A356) and an Al-Cu alloy were used as matrices in the present study. The material parameters (such as matrix and reinforcement type) and process parameters (such as mold temperature, mold speed, and melt stirring) were found to influence the gradient in the FG-AMCs. Detailed microstructural analysis of the composites in different processing conditions revealed that the gradients in the reinforcement modify the microstructure and hardness of the Al alloy. The segregated in-situ formed TiB₂ and TiC particles change the morphology of Si particles during the solidification of Al-Si alloy. A maximum of 20 vol pct of reinforcement at the surface was achieved by this process in the Al-4Cu-TiB₂ system. The stirring of the melt before pouring causes the reinforcement particles to segregate at the periphery of the casting, while in the absence of such stirring, the particles are segregated at the interior of the casting.     

西气东输工程用大口径X70输气管线用板卷的研制

宝山钢铁股份有限公司开发研制的针状铁素体型X70大口径输气管线用板卷钢已应用于西气东输管线工程.与贫珠光体(含有少量的珠光体)组织类型的X70管线钢相比,新开发的针状铁素体型X70管线钢板卷在具有高强度的同时,具有更高的低温冲击韧性、低的韧-脆转变温度以及高的抗动态撕裂能力.其优良的性能得益于具有与细小析出相交互作用的高密度位错的超低碳针状铁素体组织.