Base Metal Side Research Articles

Laser welding of ultra-high strength steel rocket engine shell

The microstructure and mechanical properties of 30Cr3-30CrMnSiA ultra-high strength steel rocket engine shell welded joint were investigated in detail. The results indicated that the microstructure of the fusion zone was martensite of columnar and equiaxial due to the fast cooling rate of the laser welding. At the as-weld (AW) state, the average grain size of the 30Cr3 base metal was 4.63 μm, which was much smaller than that of the 30CrMnSiA base metal, which averaged 6.85 μm. After the post-weld heat treatment (PWHT), all the microstructures of the base metal, fusion zone and heat affected zone (HAZ) of 30Cr3 were tempered martensite. Meanwhile, at both AW and PWHT state, the tensile specimens of the welded joints of dissimilar materials were all fractured in the 30CrMnSiA base metal side at both 25 °C and 800 °C. After the PWHT, the tensile strength of 30CrMnSiA and 30Cr3 base metal at 25 °C were 1517.4 MPa and 1795.3 MPa, respectively. The welded joints of dissimilar materials by laser welding also showed excellent tensile properties at high temperature (800 °C), because of the small average grain size.

Spray Coated Cellulose Nanofiber (CNF) Film as an Eco-Friendly Substrate for Flexible and Printed Electronics

Cellulose nanofiber is an eco-friendly nanomaterial used for fabricating various functional materials. It is an alternative for synthetic plastic and other petroleum derived materials. Due to demand of CNF film, fast and rapid method for fabrication of CNF film is required. A new method on spray coating to prepare smooth cellulose nanofiber (CNF) films was developed. In this method, spraying CNF suspension onto a smooth and polished metal surface was carried out and then allowed the spray coated wet film to dry in air under standard laboratory conditions. Spraying has notable advantages such as contour coating and contactless coating with the base substrate. The basis weight and thickness of the CNF film is tailorable by adjusting CNF suspension in spraying process. CNF film prepared via spray coating has unique two-sided surface roughness with the surface in contact with the base substrate or metal side much smoother than the air-contact side. The surface roughness is one of the controlling parameter in the application of the CNF film as a substrate for flexible and printed electronics. The RMS roughness of the two surfaces investigated by Optical Profilometry [OP] was found to be 2087 nm on the rough side and 389 nm on the spray coated side, respectively. The spray coated CNF film has ultra-high smoothness on the side exposed to the polished stainless steel surface. The factors including the size of cellulose fibrils and surface smoothness of base surface that control the roughness of the film are currently being investigated and will be discussed in this chapter. The surface smoothness requirements for substrate applications in flexible and printed electronics will be discussed.

Effect of Nb-free consumables on the microstructure and structural integrity of pressure vessel grades of dissimilar austenitic stainless steel welded joints

The research article demonstrates the role of fillers in the evolution of the microstructure and mechanical integrity of dissimilar joints of stabilized austenitic stainless steels. Pulsed direct current (PDC) gas tungsten arc welding (GTAW) technique was adopted to obtain the joints of dissimilar grades of stabilized austenitic stainless steels such as AISI 321 and AISI 347. The joints of these dissimilar grades of stainless steels were achieved using a ferritic-austenitic stainless-steel filler ER2553 and Ni-rich austenitic fillers ERNiCrMo-4, ERNiCrMo-10. Delta ferrite was observed in heat-affected areas (HAZ) on both sides of stainless steels, regardless of joints. Precipitation of Mo–Nb, Mo–W rich phases was noticed in the fusion zones (FZ) while adopting Ni-based austenitic fillers. During the tensile load, the fractures occurred on the base metal side of the AISI 321 for the Ni-based fillers and on the FZ while using the ER2553 fillers. The joint efficiencies achieved by these dissimilar joints were 103.2%, 128.11% and 116.16% for ER2553, ERNiCrMo-4 and ERNiCrMo-10 fillers respectively. The joints established with the ERNiCrMo-4 filler improved the notch's impact resistance in ambient temperature and below zero conditions compared to other weld seams.

Effect of Rotational Speed on Static and Fatigue Properties of Rotary Friction Welded Dissimilar AA7075/AA5083 Aluminium Alloy Joints

In this work, rotary friction welding processes of dissimilar AA7075/AA5083 aluminium alloy rods with the diameter of 15 mm were performed at varying rotational speeds, typically 370 to 2500 rpm. The aim of this research is to improve mechanical properties, in particular, strength and fatigue performance of the weld joints. Several experiments including macro and microstructural examinations, Vickers microhardness measurements, tensile tests, fatigue tests and residual stress measurements were carried out. Results showed that at higher rotational speeds, typically 540 rpm or above, the dissimilar AA7075/AA5083 rotary friction weld joints revealed a static fracture in the AA5083 base metal side, indicating that the joint efficiency is more than 100%. It seemed that the best weld joint was achieved at the rotational speed of 1200 rpm, in which the friction heat was sufficient to form metallurgical bonding without causing excessive flash and burn-off. In such a condition, the fatigue strength of the weld joint was slightly higher than AA5083 base metal, but it was lower than AA7075 base metal. It was confirmed that the crack origin is observed at the interface followed by fatigue crack growth towards AA5083 side, and the growth of crack seemed to be controlled by microstructure and residual stress.

Vacuum brazing TiAl intermetallics to GH3030 alloy with a multi-component Ti-based filler metal

TiAl intermetallics was vacuum-brazed to GH3030 alloy with multi-component Ti-based amorphous filler metal (Ti 36.1 Zr 11.1 V 2.8 Cu 38.9 Ni 5.6 Al 2.8 Co 2.8 , at.%). The effect of brazing temperature on the microstructure evaluation and shear strength of TiAl/GH3030 brazed joint was studied. The brazed seam presented sectionalized feature with the formation of four reaction zones. Two transition zones with linear growth formed respectively adjacent to two base metals due to elemental solid-state diffusion from the filler metal to base metals. Increasing the brazing temperature accelerated the diffusion between the filler metal and base metals. And those two transition zones thickened, as well as the middle zone composed of primary phase and (Ti, Zr)(Al, Cu, Ni) matrix. Blocky primary phase Ti(Al, Cu, Ni) 3 in middle brazed seam increased, thinning the Ti(Ni, Cu) reaction layer. The maximum shear strength of the brazed joint was obtained at 990 °C. During the shear test, the cracks of the brazed joint propagated along the interface of the transition zone/middle brazed seam at TiAl base metal side on account of the stress concentration and the formation of Ti(Al, Cu, Ni) and Ti(Al, Cu, Ni) 3 at two sides of the fractured interface. And the failed joint exhibited layered fracture surfaces and brittle fracture feature.

Development of arc welding technique to preclude microsegregation in the dissimilar joint of Alloy C-2000 and C-276

Hastelloy C-2000 and C-276 are widely used in Flue Gas Desulphurization (FGD) system and Chemical Processing Industries (CPI). Current work is focused on weld microstructure, and mechanical properties (structure-property relationship) of the dissimilar combination of alloy C-2000 and C-276. Multi-pass Pulsed Current Gas Tungsten Arc (PCGTA) welding was adopted for joining the dissimilar alloys using the filler ERNiCrMo-17. Microstructural characteristics of the weld joint were assessed by Optical and Scanning Electron Microscope (SEM). Weld interface microstructure examination revealed the presence of grain coarsening near the Heat Affecting Zone (HAZ) of the alloy C-276 side. SEM analysis shows the absence of secondary Topologically Closed Packed (TCP) phases in the Inter-Dendritic (ID) regions of the dissimilar weld. Micro-segregation of alloying elements in the weldment was assessed by Energy-Dispersive X-ray Spectroscopy (EDS). X-Ray Diffraction (XRD) analysis had been carried out to identify the phase constitution and average grain size. Strength, toughness, and hardness of the dissimilar weld were evaluated with the support of the tensile test, Charpy impact test, and Vicker’s hardness test. Tensile study showed that all the tensile fracture occurred at the base metal side of alloy C-276. The average toughness of the dissimilar alloy joint was noted about 84 J. Hardness test results indicated that fusion zone (FZ) hardness value was 6.19% and 2.27% superior to the candidates’ material (C-276 and C-2000) employed in this study. The refined grain structure and absence of microsegregation resulted in the highest hardness in the dissimilar weld FZ. Results revealed the substantiated use of PCGTA welding for the effective joining of dissimilar alloys of C-2000 and C-276 through the evaluation of metallurgical and mechanical characteristics.

Static and Fatigue Properties of Rotary Friction Welded Dissimilar AA7075/AA5083 Aluminium Alloy Joints at Various Rotational Speeds

In the present study, dissimilar rotary friction welding of AA7075/AA5083 aluminium alloy rods having diameter of 15 mm was conducted at various rotational speeds in the range of 370 to 2500 rpm. The aim of this research is to gain the best weld mechanical properties in particular weld tensile strength and fatigue performance. Several experiments were carried out including macro and microstructural examinations, microhardness measurements, tensile tests and fatigue tests combined with residual stress measurements. Results show that at higher rotational speeds, typically 540 rpm or above, the dissimilar AA7075/AA5083 rotary friction weld joints reveal static fracture in the AA5083 base metal side indicating the joint efficiency is more than 100%. It seems that the best weld joint is achieved at the rotational speed of 1200 rpm in which the friction heat is sufficient to form metallurgical bonding without causing excessive flash and burn-off shortening. In such a condition, the fatigue strength of the weld joint is slightly higher than its AA5083 base metal but it is lower compared to another AA7075 base metal. It is confirmed that the crack origin is observed at the interface followed by fatigue crack growth towards AA5083 side and the growth of crack seems to be controlled by microstructure and residual stress.

Characterization of composite laminate with copper and AISI304 made by a diffusion bonding process

The composite laminate assembly was made by stacking alternate layers of AISI304 and copper foils. The copper and AISI304 foils of 0.1 mm thick were placed one above the other and during diffusion bonding experiments. The bonding parameter temperature was varied as 850, 900 and 925 ⁰C, constant pressure of 4 MPa, and bonding time of 60 min was maintained for all the experiments. The laminated joints were characterized by optical, scanning electron microscopy for grain size measurement and phase identification. Electron microprobe analysis (EPMA) was performed at the joint region for elemental analysis across the interface and into the base metals. At the AISI304 base metal side a maximum hardness of 342.6 VHN and at the copper base metal side, it was 152.5 VHN. For the sample bonded at 925 ⁰C, the shear strength was a maximum of 72.8 MPa. X-Ray Diffraction Analysis (XRD) revealed the presence of phases γ-Fe and γ-Cu, and intermetallic compounds such as FeCu 4 , Cu 2 CrNi, sigma (σ)-phase and oxide CuO.

Characterization of Metallurgical and Mechanical Properties of Thixowelded AISI D2 and AISI 304 Steels

In this study, AISI D2 tool steel was thixowelded with AISI 304 austenitic stainless steel by using a direct partial remelting technique. The joining parameters (temperature, soaking time, and contact area) have been investigated by studying their effects on the mechanical and metallurgical properties of the thixowelded joint. The joint interfacial microstructures were investigated by optical microscopy, scanning electron microscopy equipped with an EDX analyzer, and x-ray phase analysis was performed to identify the phase evolution. Mechanical characterization was determined by tensile and micro-hardness tests. Maximum tensile strength that was achieved is 635 MPa at 1300 °C, with a 5 mm insert diameter and 10 min holding time. This represents 80% of the D2 base metal strength. The joints were fractured on the D2 base metal side close to the diffusion zone characterized by brittle fracture. Consequently, the joints also achieve a full penetration weld with a smooth and uniform hardness profile.

Correlation between Tensile Deformation Behavior and Microstructural Morphology of Nuclear Grade Austenitic Stainless Steel Weld Joints using Infrared Thermography Technique

Tensile deformation behavior of nuclear grade Austenitic Stainless Steel (SS) and its weld joints fabricated by Gas Tungsten Arc Welding (GTAW) and Activated flux Gas Tungsten Arc Welding (AGTAW) processes were studied and correlated with relevant microstructural morphologies using Infrared Thermography (IRT) technique. The microstructure of base metal showed a complete austenite phase. GTAW Fusion Zone (FZ) exhibited both primary ferrite and primary austenite mode of solidification. Meantime, AGTAW FZ exhibited only primary austenite mode of solidification A strain rate of 4.4x10-4 s-1 was used during the tensile test of the base metal and weld samples. The failure locations of the base metal, GTAW and AGTAW samples were noticed at the center of the gauge portion, the base metal side away from Fusion Line (FL) and Heat Affected Zone (HAZ) respectively. Temperature variations of the base metal and weld zones were recorded in the form of thermograms using the IR camera at the different stages of the tensile deformation. During deformation study, peak temperatures of 39.2 oC, 38.8 oC and 34 oC were observed at the base metal, GTAW and AGTAW samples respectively. The lesser peak temperature of the AGTAW sample compared to the base metal and GTAW samples indicated that the AGTAW sample undergone lesser deformation. Moreover, tensile deformation behaviors of the base metal and weld samples were correlated with their microstructural morphologies using corresponding temperature curves.

Corrosion behavior and mechanical properties of cold metal transfer welded dissimilar AA7075-AA5754 alloys

Cold metal transfer (CMT) welding is a brand-new arc welding technique which shows adequate results for welding of thin sheets and dissimilar materials. Corrosion behavior of dissimilar aluminum joints should be determined in terms of predicting the effect of welding process on the possible failures in their constructions caused by corrosive agents. The present study investigates the effect of heat input on mechanical properties and corrosion rate of AA5754-AA7075 joints welded by CMT using ER5356 filler wire. Pore formation was observed not only in the weld metal but also in the partially melted zone of AA7075 base metal due to the vaporization of zinc. Increased heat input caused over aging and zinc vaporization in AA7075 base metal, and grain coarsening in AA5754 base metal consequently decreased the tensile strength. The average tensile strength of AA7075-AA5754 joints varies between 235 and 240 MPa. The ductile fracture occurred at the AA5754 base metal side in all samples. Pitting was observed as the dominant corrosion mechanism. Corrosion resistance tended to increase with increasing heat input. Heat input values between 95 and 110 J/mm are recommended for the optimization of corrosion resistance and strength.

Impact performance and microstructures of thick TA1 titanium alloy sheets welded by vacuum electron beam

Thick TA1 titanium alloy sheets were thoroughly bonded by vacuum electron beam welding (EBW). The results indicated that microstructures in the weld zone (WZ) consisted of coarse α columnar grains, serrated α as well as needle-shaped α′; the microstructure in the heat-affected zone near the WZ side was composed of α′ and α, while the microstructure near the base metal side consisted of α″ and α. The positional relation between the notches and rolling direction had an important role in the impact performance. The EBW joint exhibited higher absorbed impact energy at the weld seam after local heat treatment. Furthermore, lots of dimples were produced on the impact fracture surfaces, exhibiting ductile fractures.

Influence of heat treatment on microstructures and mechanical properties of K447A cladding layers obtained by laser solid forming

Laser solid forming employing a paraxial powder-feeding system was developed to repair gas-turbine hot-section components composed of the non-weldable nickel-based superalloy K447A. In the present study, hot isostatic pressing, solid solution, and double-aging heat treatments were applied to research the influence of heat treatments on the forming characteristics, microstructural characteristics, and tensile properties of cladding zones obtained by laser solid forming. The results showed that cladding layers (CLs) without hot cracking or blowholes were obtained after heat treatment. Shrinkage elimination and γʹ precipitate growth were observed, MC-type carbides precipitated from the solidification grain boundary (SGB) and partly transformed into M23C6-type carbides in the CL. The hardness in CLs became uniform and nearly equal to that of the base metal (BM). The strength of the heat-treated half-BM, half-CL (HBC) specimen was nearly equal to that of the heat-treated BM specimen, but the elongation of the HBC specimen was reduced by ∼40%. In the BM side of the HBC specimen, cracks initiated at script-like carbides and extended along the grain boundaries, while in the CL side, cracks extended along the SGB with massive granular carbides, which reduced the elongation of the HBC specimen.

Investigations of the corrosion damage process of the brazed joint AISI 304L/BNi-2

Abstract One of the most frequently used material combinations to produce heat exchangers for automotive exhaust systems are vacuum brazed AISI 304L/BNi-2 components. In order to simulate the influence of condensate corrosion on such parts during service, the well-established test procedure for testing the resistance of metallic materials to condensate corrosion in exhaust gas, VDA 230-214, is used in this study. For a test duration of up to 6 weeks, miscellaneous corrosive mechanisms were observed and examined concerning their formation and progression. The corrosive attack starts at the diffusion zone on the base metal side due to the formation of chromium borides and the reduced nickel content. Between week 4 and 5, the greatest material removal was observed, which goes in line with a diameter reduction from 6.5 mm down to 5.8 mm of the load-bearing area. In this regard, the ultimate tensile strength drops down from 253.3 MPa to 147.8 MPa after 6 weeks of corrosive testing.

Microstructure and properties of a dissimilar weld between alloy 617 and A387 steel using different filler metals

In this study, microstructural and mechanical properties of a (butt) weld, joining two base metal alloys 617 and A387-Gr.11 steel, were investigated. Fusion welding was performed using gas tungsten arc welding. Three different filler metals of ERNiCrMoCo-1, ERNiCr-3, and ER309L were used to perform welding. Microstructural analysis was conducted with optical and scanning electron microscopes. Microstructural observations revealed that the extent of carbon migration and martensite phase formation in the transition zone is reduced by using filler metals of higher Ni content. For the ERNiCrMoCo-1 filler metal, unmixed zone in alloy 617 base metal side was eliminated. Microhardness, impact, and tensile tests were carried out to determine the mechanical properties of the dissimilar metal welds (DMWs). The welds made by using ERNiCrMoCo-1 filler metal resulted in highest hardness and impact energy, whereas ERNiCr-3 filler metal weld displayed the highest tensile strength, yield strength, and elongation in comparison with other fillers. Based on the results, the ERNiCrMoCo-1 filler metal was found to be the best filler metal choice for the DMWs of these two base metals.

Investigations on the microstructure and mechanical properties of dissimilar welds of inconel 718 and sulphur rich martensitic stainless steel, AISI 416

Turbine blisk and shaft assembly in aero-engines make use of dissimilar joints of Inconel 718 and martensitic stainless steel, AISI 416. The joining of these 5 mm thick aerospace alloys carried out by adopting current pulsing in Gas Tungsten Arc Welding (GTAW) has been addressed. Two Nb free consumables namely ERNiCrMo-4, ERNiCu-7 and a duplex filler ER2553 were used to join these dissimilar combinations. The weldments were systematically characterized using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). It is endorsed from the studies that the welds obtained from these fillers were free from deleterious Laves phase. Irrespective of fillers, the tensile failures were experienced at the base metal side of AISI 416. Room temperature Charpy V-notch impact test indicated that the weld joints employing ERNiCu-7 witnessed better impact toughness than other weldments. This study is highly in demand in aerospace industries and successfully addressed the choice of fillers in supressing the Laves phase.

Microstructures and their distribution within HAZ of X80 pipeline steel welded using hybrid laser-MIG welding

Large microstructure gradient in the heat-affected zone (HAZ) in the joints of large thick material welded by the hybrid laser-MIG welding technology reduces the in-service reliability and durability of the welded structure. It is of great importance to characterize and analyze how the microstructure distribution and evolution occur in the HAZ of the laser-MIG hybrid welded joints fabricated with X80 pipeline steel. In this article, the HAZ is found to comprise these characteristic zones, namely banded microstructure HAZ (BMHAZ), fine-grained HAZ (FGHAZ), transitional microstructure HAZ (TMHAZ), and coarse-grained HAZ (CGHAZ). The zone of the HAZ contains quasi-polygonal ferrite (QF), M-A component, polygonal ferrite (PF), and bainite ferrite (BF). From the base metal side towards the weld center with the decrease in the distance, the size of the M-A components decreases and its distribution is more dispersed, while the content of QF decreases in the HAZ. The average diameter of the original austenite grain increases gradually and so does the content of lath microstructures.

Stress Corrosion Cracking Behaviour of Dissimilar Welding of AISI 310S Austenitic Stainless Steel to 2304 Duplex Stainless Steel

The influence of the weld metal chemistry on the stress corrosion cracking (SCC) susceptibility of dissimilar weldments between 310S austenitic stainless steel and 2304 duplex steels was investigated by constant load tests and microstructural examination. Two filler metals (E309L and E2209) were used to produce fusion zones of different chemical compositions. The SCC results showed that the heat affected zone (HAZ) on the 2304 base metal side of the weldments was the most susceptible region to SCC for both filler metals tested. The SCC results also showed that the weldments with 2209 duplex steel filler metal presented the best SCC resistance when compared to the weldments with E309L filler metal. The lower SCC resistance of the dissimilar joint with 309L austenitic steel filler metal may be attributed to (1) the presence of brittle chi/sigma phase in the HAZ on the 2304 base metal, which produced SC cracks in this region and (2) the presence of a semi-continuous delta-ferrite network in the fusion zone which favored the nucleation and propagation of SC cracks from the fusion zone to HAZ of the 2304 stainless steel. Thus, the SC cracks from the fusion zone associated with the SC cracks of 2304 HAZ decreased considerably the time-of-fracture on this region, where the fracture occurred. Although the dissimilar weldment with E2209 filler metal also presented SC cracks in the HAZ on the 2304 side, it did not present the delta ferrite network in the fusion zone due to its chemical composition. Fractography analyses showed that the mixed fracture mode was predominant for both filler metals used.

Effect of heat input on microstructure and mechanical properties of pulsed laser welded joints in Ti6Al4V/Nb dissimilar alloys

Pulsed laser welding was used to weld dissimilar joints in Ti6Al4V/Nb alloys. The effect of heat input on the microstructural characterizations and mechanical properties of the joints was investigated. The experimental results show that underfill defects disappeared in the fusion zone (FZ) as the heat input increased. No intermetallic compounds were formed in the FZ, but a dendritic zone of Ti-rich phases and an island zone of Nb-rich phases were present for all welded joints, indicating that composition segregation occurred in the Ti6Al4V/Nb dissimilar joint. Moreover, the microstructure and mechanical heterogeneity in the FZ of the welded joint increased with increasing heat input. The microhardness of the island area was lower than that of the dendritic zone in the FZ, because it possessed higher levels of Nb. The results of the tensile tests show that the joints fractured at the Nb base metal side, suggesting that the strength of the FZ is higher than that of the Nb base metal.

Improvement in limiting drawing ratio of aluminum tailored friction stir welded blanks using modified conical tractrix die

In the present work, aluminum tailor friction stir welded blanks (TFSWBs) of dissimilar grade and gauge combinations were fabricated successfully with optimized parameters. The tensile tests of TFSWBs were conducted perpendicular to the weld orientation to confirm the weld quality, and it was found that the failure occurred in the weaker base metal side. Subsequently, the limiting drawing ratios (LDR) of the base metals as well as TFSWBs were evaluated and compared using a conventional cylindrical die (CCD) and a modified conical tractrix die (MCTD) setup. Approximately, 27% and 14% improvements in LDR were recorded respectively for the dissimilar grade and the dissimilar gauge TFSWBs while using the MCTD setup. The finite element (FE) simulations of the improvements in LDR were carried out using LS-DYNA solver. For identifying the failure steps, the thickness true strain gradient (TTSG) method was incorporated successfully in the FE model. The predicted LDR and thickness distribution of the deep drawn cups of TFSWBs and the base metals were validated with the experimental data. Also, the strain envelope progression profiles and thinning development predicted from the validated FE models were analyzed rigorously to get an insight into the improvement in the material flow during deep drawing operation using MCTD.