Thermo-Calc Simulation Research Articles

Development and Mechanical Characterization of a CoCr-Based Multiple-Principal-Element Alloy

The development and mechanical characterization of a CoCr-based multiple-principal-element alloy are presented and discussed. In this work, ab initio synthesis and mechanical characterization of the (CoCr)100-x(TiNbZr)x (x = 0, 48 60, 78 and 100 % at) alloy family is reported; these include the calculation of thermodynamic parameters such as mixing entropy (ΔSmix), mixing enthalpy (ΔHmix), valence electron concentration (VEC), Ω and δ factors. The alloys were melted in a vacuum arc furnace; rod-shaped ingots were produced by suction casting. Phase characterization was carried out using optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction. Mechanical characterization was done via compressive and hardness tests. Calculation of phase diagrams was performed using Thermo-Calc © software. Yang’s model for phase prediction predicted a BCC solid solution. Multicomponent simulations predicted a more complex structure, with Laves (C14 and C15), Theta (C16), BCC 1, 2 and 3, Mu, CoTi2, CoZr3 and TiZr2. Contrary to Yang’s model for phase prediction, the experimentally obtained phases agreed reasonability well with those obtained by the Thermo-Calc simulation. The suction cast process cooling rate suppressed the nucleation and growth of some equilibrium phases, i.e., Laves (C14) or BCC 3 for the (CoCr)100-x(TiNbZr)x (x = 0, 48 60, 78 and 100 % at) alloys. The hardness test results were strongly related to the intermetallic phase formation, showing an increase of 331% with the x = 78 alloy. The BCC 1 phase played an important role in the yield strength behavior, as the (CoCr)22(TiNbZr)78 alloy, with a considerable amount of this phase, showed the highest yield strength value.

Microstructure, mechanical and corrosion study of friction stir processed Inconel 625 additive layers deposited via wire arc direct energy deposition

This study explores the application of friction stir processing (FSP) as an effective post-deposition surface treatment technique for improving the mechanical and corrosion properties of wire arc direct energy deposited (WA-DED) Inconel 625 additive layers. The coarse and cube-oriented microstructure observed in as-built Inconel 625 components results in anisotropic mechanical properties. The non-equilibrium solidification in WA-DED Inconel 625 leads to severe micro-segregation of alloying elements, forming large Nb and Mo-rich Laves and carbide phases in the inter-dendritic areas. This causes a heterogeneous distribution of vital alloying elements within the γ-Ni matrix of the material, adversely affecting its mechanical properties and corrosion resistance, thereby restricting the utility of this manufacturing technique in critical applications. The incorporation of FSP has been observed to successfully eradicate the presence of typical coarse and highly oriented microstructure through grain refinement, achieving a more uniform microstructure. Through severe plastic deformation (SPD), coarse eutectic phases are broken down and redistributed within the γ-Ni matrix, enhancing the uniformity of material properties. The research thoroughly investigates the changes in microstructure, mechanical performance, and corrosion resistance of both WA-DED and FSP-enhanced WA-DED Inconel 625 samples. A Thermo-Calc simulation using the classical Scheil model was conducted to understand the solidification pathway and the formation mechanism of the Laves phase in the WA-DED sample. The grain size was significantly reduced by 98.23%, from 138 µm in the WA-DED sample to 2.44 µm in the stir zone (SZ) of the FSP-treated area, due to dynamic recrystallization (DRX), particle-stimulated nucleation (PSN), and the Zener pinning effect. This grain refinement led to remarkable enhancements in the yield strength (YS) by approximately 113%, ultimate tensile strength (UTS) by about 37% and micro-hardness by around 60% compared to the WA-DED sample. In a 3.5 wt% NaCl solution, the FSP-treated sample demonstrated superior corrosion resistance by forming a stable, thicker passive film than the as-built sample. The results of this study will offer valuable insights into utilizing the FSP technique as post-weld surface treatment of WA-DED deposited IN625 superalloy.

Thermodynamic Analysis of Al-Ni, Al-Cu Alloys System Using Calphad Method

Abstract: The CALPHAD technique, in conjunction with the PBIN database, is employed to conduct a thorough thermodynamic analysis and assessment of the binary alloy systems Al-Cu and Al-Ni. This study explores the thermodynamic properties, including phase diagrams, Gibbs free energies, and thermodynamic molar activities across the entire compositional range. The temperature maintained for assessment is 2000-2050 K. The doping characteristic of the AL-Ni binary system is more epitaxial and useful for doping industries. The correspondence of Raoult’s law is more precise in the Al-Ni binary alloy system due to its better doping characteristics. The entropy and the enthalpy of both systems increase. The greater decrease in the Gibbs curve and activity predicted the more stability of the alloying system Al-Ni. Within the Al-Ni system, a composition range of 0.4-0.6 mole percent at a temperature of 2050 K is identified as the most stable, contrasting with the Al-Cu system, which exhibits the least stability. The lattice vibrations mode and Brillion zone growth during alloying contribute to highly epitaxial characteristics, with pure and sharp attractive interactions among alloying elements. Negative deviation from ideality in activity is observed in the Al-Ni system, further supporting its increased stability. This is attributed to the lower Gibbs energy and higher enthalpy accordance. Both Al-Cu and Al-Ni binary systems show the highest level of equilibrium and stability. The enthalpy values of both alloying systems gradually increase with temperature. In the solid era of both binary alloy systems, Al-Cu and Al-Ni, the ferrite phase is identified as the stable phase. The most stable ferrite phase, capable of withstanding the highest temperatures, holds promise for applications in industrial sectors and materials metallurgy. Keywords: Thermodynamic properties, CALPHAD method, Thermo-calc simulation package, Alloys.

In-situ synchrotron X-ray diffraction investigation of martensite decomposition in Laser Powder Bed Fusion (L-PBF) processed Ti–6Al–4V

Laser powder bed fusion (L-PBF) processed Ti–6Al–4V components present two substantial challenges: the presence of tensile residual stress and brittleness of the as-fabricated component due to the formation of the martensite (α′) phase. Industrially, post-heat treatment is performed to improve the quasi-static mechanical properties of the Ti–6Al–4V component through martensite (α′) decomposition and residual stress relaxation. However, detailed insights into the martensite decomposition and stress relaxation mechanisms are still lacking. To address this, in-situ high-energy synchrotron x-ray diffraction (HEXRD) was employed to simultaneously track: (I) martensite (α′) decomposition into a mixture of hexagonal α and body-centered cubic β phases, (II) residual stress relaxation process during heating. Rietveld refinement of 2D diffraction patterns recorded over a temperature range spanning from 25 to 1000°C revealed a three-stage evolution in the α′ unit cell parameters. Unit cell parameter analysis combined with the phase fraction analysis based on the diffraction patterns and the chemical composition profiles predicted by Thermocalc simulation gave detailed insight into the martensite (α′) decomposition process. In Stage 1 (until 375°C), the α′ phase unit cell exhibited linear expansion without indications of any phase transformation or stress relaxation. Upon commencement of stage II at 375°C, an increased expansion rate of the martensite (α′) unit cell was observed, attributed to the enhanced outward diffusion of vanadium (V), succeeded by β phase nucleation at 575°C. Simultaneously, during stage II, residual stress relaxation was observed at both macro and micro scale, culminating in a stress-free state achieved at approximately 750–800°C. Lastly, α-to-β phase transformation was observed in stage 3. The thermal evolution of the hexagonal unit cell dimensions was compared between martensitic and mill-annealed α+β microstructures. This comparison unraveled the link between the initial microstructure and the thermal expansion behavior of the hexagonal α′ and α phase.

Effect of the Cu/Mg Ratio on Mechanical Properties and Corrosion Resistance of Wrought Al–Cu–Mg–Ag Alloy

The present study aimed to investigate the influence of magnesium (Mg) on the mechanical properties and corrosion behavior of wrought Al–4Cu–xMg–0.6Ag alloys. The results from Optical Microscope, SEM, XRD analysis, and Thermo-Calc simulation were used to identify the microstructure formed after the aging process. Testing for hardness and tensile strength was conducted, in addition to corrosion testing. It was found that Mg significantly impacts the hardness of the alloys, with a high Mg content (low Cu/Mg ratio) increasing the hardness but reducing the tensile strength and ductility. This study attributed this to the formation of the S phase, which is dependent on both the quantity in the bulk and the size of the phase. The grain size was found to be finer with a higher Mg content, since the particle size inhibits grain growth during the artificial aging process. Counterintuitively, the corrosion activity was reduced in the high-Mg-content alloy due to its large particle size and the reduced galvanic cell effect. This study highlighted the importance of considering the effects of Mg on the mechanical properties and corrosion behavior of Al–Cu–Mg–Ag alloys.

Flow Behavior and Microstructure of Hot-Worked Fe-30.9Mn-4.9Al-4.5Cr-0.4C and Fe-21.3Mn-7.6Al-4.3Cr-1C Low-Density Stainless Steels

Two as-cast low-density steels grades (austenite-based duplex Fe-30.9Mn-4.9Al-4.5Cr-0.4C and austenitic Fe-21.3Mn-7.6Al-4.3Cr-1C) with an initial dendritic microstructure were subjected to hot working conditions to understand the influence of deformation parameters on flow behavior and microstructural evolution. The alloys were produced using electric arc melting, and their phase constituents were determined using optical microscopy and X-ray diffraction analysis. This was then corroborated with the phase predicted from Thermo-Calc simulation. The as-cast alloys were machined to 10 × 10 × 7 mm specimen configurations for rectangular axial testing on the Gleeble 3500 thermomechanical simulator. The samples were deformed to a total strain of 0.5 at different deformation temperatures (800, 900, and 1000 °C) and strain rates (0.1 and 5 s−1). Thereafter, a hardness test was conducted on the deformed samples, and post-deformed microstructures were analyzed using optical and scanning electron microscopes. The results showed that the alloys’ dendritic structures were effectively transformed at temperatures below 1000 °C regardless of the strain rate. At all deformation conditions, the peak flow stress of Fe-21.3Mn-7.6Al-4.3Cr-1C alloy was at least 50% higher than that of Fe-30.9Mn-4.9Al-4.5Cr-0.4C alloy owing to the higher carbon content in the austenitic low-density stainless steel. The hardness of all the deformed samples was superior to that of the as-cast samples, which indicates microstructural reconstitution and grain refinement in the alloys. Dynamic recrystallization, dynamic globularization, and dynamic recovery influenced the softening process and the microstructural changes observed in the alloys under different deformation conditions.

Microstructure and Mechanical Property of Al6Si2Cu Alloy Subjected to Double-Solution Heat Treatment

This study aims to develop the mechanical properties of the Al6Si2Cu aluminum alloy through the double-solution treatment. In addition to the Al matrix, large amounts of coarse eutectic Si, Al2Cu intermetallic, and Fe-rich phases were generated through thermo-calc simulation in agreement with the equilibrium phases. The eutectic Si phase is fragmented and spheroidized by the solution treatment as the heat treatment temperature and time increase. The Al2Cu intermetallic phase is dissolved into the Al matrix, resulting in an increase in both strength and elongation. The second-step solution temperature at 525 °C should be an optimum condition for enhancing the mechanical properties of the Al6Si2Cu aluminum alloy.

Investigation of formation of precipitates and solidification temperatures of ferritic stainless steels using differential scanning calorimetry and Thermo-Calc simulation

Investigation of formation of precipitates and solidification temperatures of ferritic stainless steels using differential scanning calorimetry and Thermo-Calc simulation

Phase constitution, microstructure and mechanical properties of a Ni-based superalloy specially designed for additive manufacturing

In this study, a kind of Ni-based superalloy specially designed for additive manufacturing (AM) was investigated. Thermo-Calc simulation and differential scanning calorimetry (DSC) analysis were used to determine phases and their transformation temperature. Experimental specimens were prepared by laser metal deposition (LMD) and traditional casting method. Microstructure, phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy (SEM), transmission scanning electron microscopy (TEM), X-ray diffraction (XRD) and tensile tests. The results show that this alloy contains two basic phases, γ/γ’, in addition to these phases, at least two secondary phases may be present, such as MC carbides and Laves phases. Furthermore, the as-deposited alloy has finer dendrite, its mean primary dendrite arm space (PDAS) is about 30–45 μm, and the average size of γ’ particles is 100–150 nm. However, the dendrite size of the as-cast alloy is much larger and its PDAS is 300–500 μm with secondary and even third dendrite arms. Correspondingly, the alloy displays different tensile behavior with different processing methods, and the as-deposited specimen shows better ultimate tensile stress (1,085.7±51.7 MPa), yield stress (697±19.5 MPa) and elongation (25.8%±2.2%) than that of the as-cast specimen. The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites, γ’, and Laves phase, and the segregation of elements, etc. Such important information would be helpful for alloy application as well as new alloy development.

Effect of FeO Content on Foaming and Viscosity Properties in FeO-CaO-SiO2-MgO-Al2O3 Slag System

The foaming process is an important part of the electric arc furnace (EAF) steelmaking process. It can promote thermal efficiency and reduce refractory consumption. FeO is a key material used during the foaming process. Unlike with other components used in forming foaming slag, the amount of FeO can be controlled by oxygen or carbon injection. Therefore, adjusting the content of FeO is the most economical foaming mode adopted for the EAFs steelmaking process. In this study, the influence of FeO content on the physical properties of slag was discussed. The melting temperature of the slag was evaluated using three methods: viscosity experiment, using Thermo-Calc simulation software, and high-temperature optical method. The experimental results revealed that the viscosity of slag increases as FeO content decreases. The results also revealed that foam height ratio exhibited a positive correlation with the viscosity of slag.

Solidification characteristics and as-cast microstructures of a Ru-containing nickel-based single crystal superalloy

The solidification characteristics and as-cast microstructures of a Ru-containing nickel-based single crystal superalloy were systematically investigated through thermal analysis, Thermo-Calc simulation, the planar interface solidification experiment, and the directional solidification quenching experiment. The main solidification transition temperature, segregation behavior, and solidification path were analyzed, and the microstructure evolution and phase formation mechanism were also discussed. The solidification began with the formation of primary γ dendrites (L → γ). Then Ni, Al, Ta, and Ru were enriched in the residual liquid, resulting in the precipitation of β-NiAl phase (L → β-NiAl). As the β-NiAl phase grew, the content of Ta gradually increased while the content of Al gradually decreased. Thus, the peritectic γ′ phases were precipitated on the surface of β-NiAl phase and coarsened by the incomplete peritectic reaction (L + β-NiAl → peritectic γ′ + β-NiAlResidual). The Al content further decreased and the Ta content further increased with the precipitation of the peritectic γ′ phase, leading to the formation of γ/γ′ eutectics on the surface of the γ dendrites or directly from liquid (L → γ/γ′ eutectic). Since the precipitation of β-NiAl phase and the subsequent incomplete peritectic reaction, Cr, Co, Mo, W, and Re were rejected into the residual liquid in the vicinity of β-NiAl phase, providing conditions for the nucleation of the TCP(R) phases (L → R). The wide freezing range of the alloy might be the cause of the severe micro-segregation and the precipitation of some secondary phases in the interdendritic regions.

Characterization of the microstructure, microsegregation, and phase composition of ex-situ Fe\u2013Ni\u2013Cr\u2013Al\u2013Mo\u2013TiCp composites fabricated by three-dimensional plasma metal deposition on 10CrMo9\u201310 steel

Quaternary powder mixtures yNi–20Cr–1.5Al–xTiCp (y = 78.5, 73.5, 68.5; x = 0, 5, 10) were deposited on ferritic 10CrMo9–10 steel to form on plates ex-situ composite coatings with austenitic-based matrix. Plasma deposition was carried out with various parameters to obtain eight variants. The microstructure, chemical composition, phase constitution, phase transformation temperatures, and microhardness of the two reference TiCp-free coatings and six ex-situ composites were investigated by X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, thermodynamic simulation, and Vickers microhardness measurements. All composites had an austenite matrix with lattice parameter a = 3.5891–3.6062 Å, calculated according to the Nelson–Riley extrapolation. Microstructural observations revealed irregular distribution of TiCp in the composites. Large particles generally occurred near the external surface due to the acting buoyancy effect, whereas in the interior smaller particles, with an equivalent radius around 0.2–0.6 μm, were present. Due to initial differences in the chemical composition of powder mixtures and also subsequent intensive mixing with the low-alloy steel in the liquid pool, the matrix of the composites was characterized by various chemical compositions with a dominating iron concentration. Interaction of TiCp with matrix during deposition led to the formation of nano-precipitates of M23C6 carbides at the interfaces. Based on the ThermoCalc simulation, the highest solidus and liquidus temperatures of the matrix were calculated to be for the composite fabricated by deposition of 73.5Ni–20Cr–1.5Al–5TiCp powder mixture at I = 130 A. The mean microhardness of the TiCp-free coatings was in the range 138–146 μHV0.1, whereas composites had hardnesses at least 50% higher, depending on the initial content of TiCp.

Solidification behavior and segregation characteristics of high W-content cast Ni-Based superalloy K416B

The solidification behavior of high W-content cast Ni-Based superalloy K416B has been investigated by DTA measurement, isothermal solidification experiment, and Thermo-calc simulation. The element segregation characteristic during solidification was also analyzed by EPMA. The results show that the solidification path of K416B can be summarized as follows: L → L + γ (1371 °C); L → L + γ + M6C (1370 °C); L → L + γ +MC (1332 °C); L → L + eutectic (γ + γ′) (1286 °C); L → MC (High Hf) (1147 °C). During the crystallize of primary γ dendrite, W and Co were enriched in the solid phase, while Cr, Al, Ti, Nb and Hf were enriched in the residual liquid. The positive segregation elements piled up at the remaining liquid promoted the formation of MC carbides and eutectic (γ + γ′). MC carbides precipitated at the interdendritic region and broke the residual liquid network, eutectic (γ + γ′) seemed instability and easily translated into eutectic γ′ by the remelting of γ phase and the coarsening of γ′ phase during subsequent cooling. The solidification terminated by the formation of MC (High Hf) phase.

On the substitution of vanadium with iron in Ti–6Al–4V: Thermo-Calc simulation and processing map considerations for design of low-cost alloys

Two basic cost reducing concepts, manipulation of alloy chemistry and optimisation of the hot working process, were adopted in developing low-cost experimental titanium alloys that may be suitable for land-based applications. Iron, a low-cost beta stabilising element in titanium alloys, was used as a partial and full replacement for vanadium in ASTM grade 5 Ti–6Al–4V. Thermo-Calc simulations were first done on the Ti–6Al-xV-yFe alloy compositions (for y = 4 – x and x = 1–3) to predict the amounts of phases and the β-transus temperatures. Thereafter, the compacted powders of the different experimental alloys were melted and allowed to solidify in the electric arc furnace cold copper hearth. Optical and scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterise the alloys. Also, the hardness of the low-cost alloys was measured and compared to commercial Ti–6Al–4V. The Ti–6Al–1V–3Fe alloy was subjected to hot compression testing at various temperatures (750–950 °C) and strain rates (1-10 s-1) on a Gleeble 3500 thermomechanical simulator. Processing maps and microstructural validation were used to define the most suitable processing conditions. The stress exponent and apparent activation energy were also calculated using a hyperbolic-sine equation. The results show that the low-cost alloys with partial substitution of vanadium with iron contained only α-Ti and β-Ti phases with no TiFe phase. The hardness of the alloys increased with increase in iron addition. The stress exponent “n” value was less than 5 indicating that flow softening was not solely driven by dynamic recovery. The optimum processing conditions for hot working were found at ~900 °C and 0.1 s-1 strain rate. The alloy generally had a large processing window with the softening process controlled by mechanisms such as dynamic recovery, dynamic recrystallisation of prior beta grains, and dynamic alpha lath globularisation. In the region of 750–780 °C and 1.5–10 s−1 an area of unstable deformation was established which should be avoided during processing. This work shows that low-cost α+β titanium alloys containing iron can be manufactured using traditional ingot metallurgy techniques and loss of material due to processing-induced defects can be minimised or avoided during primary conversion process such as forging and rolling.

Towards the development of experimental (α + β) Ti-Al-V-Fe alloys

The influence of partial substitution of vanadium with iron and the reduction of aluminium content on the microstructure and hardness of low-cost α + β titanium alloys was evaluated using Thermo-calc simulation, scanning electron microscopy and Vickers hardness testing. The results show that Thermo-calc predictions and microstructural analysis were in good agreement. The beta phase fraction increased with iron addition and no intermetallic phase was found in alloys having both iron and vanadium as beta stabilising elements. The hardness of the low-cost alloys increased with iron content but commercial Ti-6Al-4V alloy has superior hardness in comparison with the low-cost alloys containing 4.5 wt% aluminium and ≤2 wt% Fe.

Atomic-scale study on the mechanism of formation of reverted austenite and the behavior of Mo in a low carbon low alloy system

The mechanism of formation of reverted austenite in a low carbon low alloy system was comprehensively studied by 3D atom probe tomography and Thermo-Calc simulation. It was observed that low C-content provided the condition for nucleation of reverted austenite at lath boundaries, while the alloying elements, Mn, Ni and Cu led to the growth of reverted austenite. Mo provided diverse impact on mechanical properties of steel at high temperature. (1) The diffusional direction of Mo atoms was controlled by the partitioning of Mo; (2) MoC co-segregation layers, nano MoC clusters, nano Mo clusters and MoC precipitates were formed at two-phase interfaces; (3) Mo formed nano MoC clusters and MoC precipitates at lath boundaries or in the matrix; (4) Mo promoted the formation of Nb carbides and was dissolved in carbides to produce (NbxMo1-x)C precipitates. High resolution transmission electron microscopy images of (NbxMo1-x)C precipitates showed that they had face-centered cubic structure and the lattice constant was in the range of 0.440–0.445 nm. Nano Cu precipitates were observed in reverted austenite. MoC co-segregation layers, nano MoC clusters, nano Mo clusters and MoC precipitates formed at γ/α interfaces effectively enhanced the grain boundary strength. Nano MoC clusters, MoC precipitates and (NbxMo1-x)C precipitates in the matrix effectively pinned dislocations and prevented movement of dislocations. The combined effect led to good fire resistance and heat resistance properties of studied steel.

Influence of Chemical Composition on the Mechanical and Microstructural Properties of High Strength Steel Weld Metals Submitted to PWHT

The development of new filler metals for offshore industry is challenging because high strength and toughness levels are required after post-welding heat treatment (PWHT) is applied to reduce residual stresses. The higher chromium contents added to the chemical composition of welding consumables to attain the required ultimate tensile strength are usually associated with reduced toughness. This work presents a comparative analysis of the behavior of two high strength steel weld metals with different Cr–Mo and Mn–Ni additions that were submitted to PWHT. Weld metals obtained by shielded metal arc welding process were evaluated using mechanical tests (Charpy-V notch and Vickers microhardness) and microstructural analysis (scanning electron microscopy and electron backscattered diffraction) conducted in samples removed from the center line of weld deposits, both in the as-welded and heat-treated (600 °C for 1 h) conditions. Although similar results were obtained in the as-welded condition, different behaviors were observed after PWHT. While impact toughness for Cr–Mo additions was reduced by carbide precipitation, as predicted by thermo-calc simulation, weld metal based on Ni–Mn addition exhibited improvements after PWHT because the predominantly martensite microstructure was tempered. This makes the latter more appropriate for weldments submitted to PWHT.

Prediction of good glass forming ability in amorphous soft magnetic alloys by thermocalc simulation with experimental validation

Alloys in a (Fe70Ni30)80(B–Si–Nb)20 system, with good glass forming ability (GFA), were identified using Thermocalc software to simulate liquidus temperatures (T's) and solidification ranges (areas between the liquidus and solidus in a binary phase diagram,a line at fixed T). A region with excellent GFA was identified at 14–18% B and 0–7% Si with the balance Nb, showing minima in liquidus and solidification range. A region with a solidification range minimum, but no corresponding liquidus minimum was identified at 3–8% B and 5–10% Si but had lower GFA. A shallow liquidus minimum, with no minimum in solidification range, at 3–5% B and 1–3% Si had the lowest GFA and did not produce amorphous material. Measured GFA was ranked using parameters Trg, ΔTxg, and γm, defined herein. Only the reduced glass transition temperature, Trg, was predictive for the alloys. Differential Scanning Calorimetry (DSC) data showed liquidus T's to agree. Curie temperatures, Tc's were observed to increase with B/Nb ratio. Simulations of liquidus and solidification range for alloys with 18 and 15% glass formers do not show regions with minima in both, indicating good GFA is not expected.

Microstructural characterization and mechanical properties of K-TIG welded SAF2205/AISI316L dissimilar joint

Motivated by increasing productivity and cost-effectiveness, the feasibility of Keyhole Tungsten Inert Gas (K-TIG) welding for joining SAF2205/AISI316L dissimilar materials was presented. Single pass autogenous welding was achieved on 5.6 mm thick plates at a speed of 35 cm/min without using any filler materials and edge preparation. In-depth investigation into the weld was conducted by optical microscope, scanning electron microscope, Thermo-Calc simulation, microhardness, tensile test and impact toughness test. The results show that in order to produce defect free dissimilar joint, the torch deviation should be kept at zero to one mm towards AISI316L side. The austenite fraction increased with torch deviation shifted from SAF2205 side to AISI316L side, along with the variation in ferrite morphology from massive type to lath shape. Defect free joints possess better tensile properties than AISI316L base metal, indicating sufficient strength level for such dissimilar joint. Poorer toughness of the samples with 1 mm torch deviation towards SAF2205 side and 2 mm deviation towards 316L side is a result of imbalanced phase structure, ferritic-asutenitic solidification mode as well as harmful precipitates in the weld. It has been demonstrated that the K-TIG welding process offers an efficient way to produce sound and high quality dissimilar joint between SAF2205 and AISI316L, with 0–1 mm torch deviation towards 316L side being the desired options in terms of overall material properties.

SIMA Processing of Cu34wt.%Zn2wt.%Pb Brass Alloy

Effects of SIMA processing on size and shape of primary solid particles of Cu34wt.%Zn2wt.%Pb brass alloy was investigated. The optimal temperature for semisolid processing of the alloy was found to be around 890 °C using Thermo-calc simulation software. Liquid fraction sensitivity of the alloy around this temperature is 0.012. The results indicated the formation of non-dendritic microstructure even after 1 min holding of 10% cold worked sample at 890 °C. Sphericity of the primary solid particles increased by increasing the cold working ratio and holding time. The smallest size (103 μm) and highest shape factor (0.84) of the primary solid particles were achieved at 30% cold working ratio and 5 min holding time.