Secondary Dendrite Arm Spacing Research Articles

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

Austenite grain growth in tailored cooling rate experiment designed by numerical simulation for peritectic steel

The heat transfer model for steel solidification in Al2O3 crucial and permanent mold by finite element method was developed and validated by temperature measurement. The multi-gradient operation was novelly designed, and the tailored cooling rate in range of 0.1–10 °C/s was obtained at the target location. The simulation aided experiment with the large-sized samples was carried out, and the local cooling rate was verified by secondary dendrite arm spacing. The size of austenite grain decreases slightly as cooling rate increases from 0.15 °C/s to 0.31 °C/s, and then increases dramatically in the range of 0.31–0.48 °C/s, finally decreases with cooling rate increasing further to 9.76 °C/s. The relationship between austenite grain size and cooling rate was logarithmically regressed in the range of 0.48–9.76 °C/s, in which the kinetic equations on basis of cooling experiment and continuously cast slab can also work. However, the grain size decrease in 0.15–0.31 °C/s and then increase in 0.31–0.48 °C/s cannot be described. Based on the mechanism of peritectic solidification, the austenite grain growth is mainly controlled by diffusion at a low cooling rate smaller than 0.31 °C/s, and the final grain size is less than 1.0 mm. At a medium cooling rate between 0.48 and 3.60 °C/s, austenite grain growth is accelerated by the energy stored during massive type peritectic transformation previously, and the grain size is between 1.7 and 2.9 mm. At high cooling rate larger than 9.76 °C/s, austenite grains grow to about 0.9 mm in columnar shape. The time for grain growth is not adequate, although addition energy storage by massive transformation can also occur. The critical cooling rate for the onset of massive type peritectic transformation in the large-sized sample is between 0.31 and 0.48 °C/s. The growth velocity in the isothermal experiment is much smaller than that in continuous cooling process, confirming that the austenite grain evolution is significantly affected by previous peritectic solidification.

Effects of Pressure on Nitrogen Content and Solidification Structure during Pressurized Electroslag Remelting Process with Composite Electrode

The nitrogen content and solidification structure of the 1Mn18Cr18N ingots produced by the customized laboratory‐scale vacuum induction melting furnace and the pressure electroslag remelting furnace (PESR) with novel composite electrode under different pressure and the same power consumption are compared and studied. The results show that there are perfectly uniform radial chromium and nitrogen profiles during the PESR process. The nitrogen uptake reaction in the PESR process with composite electrode takes place on the liquid metal film on the electrode. Nitrogen uptake could be improved by increasing the nitrogen partial pressure. In addition, the basin depth at a pressure of 0.1 and 1.22 MPa is about 41 and 38 mm, the angle of the grains with respect to the vertical axis is 35° and 31°, respectively. The flat metal basin profile resulted from the thermal resistance at the slag–mold interface decreasing with increasing pressure. Primary and secondary dendritic arm spacing (PDAS and SDAS) variations exhibit an increasing and subsequently decreasing the trend as they move further away from the center in a horizontal direction. Both PDAS and SDAS decrease with increasing pressure from 0.1 to 1.22 MPa.

Uneven distribution of cooling rate, microstructure and mechanical properties for A356-T6 wheels fabricated by low pressure die casting

Complex aluminum alloy part prepared by low pressure die casting (LPDC) usually has unevenly distributed microstructure and mechanical properties, which is related to the cooling conditions. To investigate the uneven characteristics of cooling rate, microstructure and mechanical properties of LPDC-fabricated A356-T6 wheels, the typical positions (including hub, spoke, outer flange, rim and inner flange) were selected to calculate the cooling rate by casting simulation. Then, the microstructure, mechanical properties, X-ray result and element content of these positions were analyzed in detail. The result shows that, the secondary dendrite arms spacing (SDAS), eutectic silicon and β-Fe phase have the largest size at hub, and the eutectic silicon is plate-shaped when the cooling rate is 10 K/min, which results in poor ultimate tensile strength (UTS, 192 MPa) and elongation (2.1 %). While at the cooling rate of 100 K/min, refined microstructure, the disappearance of β-Fe phases and the elimination of defects result in good mechanical properties of the outer flange. The UTS and elongation exceed 250 MPa and 13 %, respectively. The rim is more prone to occur shrinkage defects at high cooling rate, which results in mechanical properties that do not meet expectations. Furthermore, the Si, Mg, and Fe elements also exhibit uneven distribution in different positions of LPDC-fabricated A356-T6 wheels. The maximum deviation of Si element between the actual content and the standard content is as high as 21 %.

The effect of melt thermal-rate treatment on precipitation hardening and mechanical properties of Al–Si–Mg alloys

In this study, we investigate the age-hardening behavior and mechanical properties of direct chill (DC)-cast Al–10Si-0.35 Mg alloys subjected to melt thermal rate treatment (TRT). Our findings reveal that TRT refines the microstructure and precipitation morphology. Grain analysis indicates the prevalence of twin dendritic grains in both TRT and non-TRT (NTRT) alloys during casting, with the TRT billet exhibiting smaller grains. The microstructural analysis demonstrates that TRT reduces the size of secondary dendrite arm spacing and eutectic phases while ensuring a uniform distribution of intermetallic particles. The precipitation mechanism in both alloys remains consistent, with the TRT alloy exhibiting a higher density of fine precipitates. Additionally, we observe a novel coprecipitation mechanism of Si and β″ phase, attributed to a lower misfit between (003)β″ and (011)Si compared to that between (003)β″ and (0 2‾ 0)Al. Furthermore, the TRT alloy displays slower precipitation kinetics due to homogeneous solute distribution, resulting in higher activation energy for precipitation nucleation. Consequently, a single age-hardening peak is observed in TRT alloys during aging. TRT alloys exhibit higher hardness and tensile strength after artificial aging at 190 and 210 °C, while maintaining comparable elongation to NTRT alloys. Theoretical calculations of precipitation strengthening also show higher values for TRT alloys, consistent with experimental results. Thus, our findings comprehend the underlying mechanisms of melt treatments crucial for improving precipitation hardening behavior and mechanical properties of Al–Si–Mg alloys.

Effect of Casting Process and Thermal Exposure on Microstructure and Mechanical Properties of Al-Si-Cu-Ni Alloy.

This paper employed squeeze-casting (SC) technology to develop a novel Al-7Si-1.5Cu-1.2Ni-0.4Mg-0.3Mn-0.15Ti heat-resistant alloy, addressing the issue of low room/high temperature elongation in traditional gravity casting (GC). Initially, the effects of SC and GC processes on the microstructure and properties of the alloy were investigated, followed by an examination of the evolution of the microstructure and properties of the SC samples over thermal exposure time. The results indicate that the SC process significantly improves the alloy's microstructure. Compared to the GC alloy, the secondary dendrite arm spacing of the as-cast SC alloy is refined from 50.5 μm to 18.5 μm. Meanwhile, the size and roundness of the eutectic Si phase in the T6-treated SC alloy are optimized from 11.7 μm and 0.75 μm to 9.5 μm and 0.85 μm, respectively, and casting defects such as porosity are reduced. Consequently, the ultimate tensile strengths (UTSs) at room temperature and at 250 °C of the SC alloy are 5% and 4.9% higher than that of GC alloy, respectively, and its elongation at both temperatures shows significant improvement. After thermal exposure at 250 °C for 120 h, the morphology of the residual second phase at the grain boundaries in the SC alloy becomes more rounded, but the eutectic Si and nano-precipitates undergo significant coarsening, resulting in a 49% decrease in UTS.

Study on the Effect of Pressure on the Microstructure, Mechanical Properties, and Impact Wear Behavior of Mn-Cr-Ni-Mo Alloyed Steel Fabricated by Squeeze Casting

ZG25MnCrNiMo steel samples were prepared by squeeze casting under pressure ranging from 0 to 150 MPa. The effects of pressure on the microstructure, low-temperature toughness, hardness, and impact wear performance of the prepared steels were experimentally investigated. The experimental results indicated that the samples fabricated under pressure exhibited finer grains and a significant ferrite content compared to those produced without pressure. Furthermore, the secondary dendrite arm spacing of the sample produced at 150 MPa decreased by 45.3%, and the ferrite content increased by 39.1% in comparison to the unpressurized sample. The low-temperature impact toughness of the steel at −40 °C initially increased and then decreased as the pressure varied from 0 MPa to 150 MPa. And the toughness achieved an optimal value at a pressure of 30 MPa, which was 65.4% greater than that of gravity casting (0 MPa), while the hardness decreased by only 6.17%. With a further increase in pressure, the impact work decreased linearly while the hardness increased slightly. Impact fracture analysis revealed that the fracture of the steel produced without pressure exhibited a quasi-cleavage morphology. The samples prepared by squeeze casting under 30 MPa still exhibited a large number of fine dimples even at −40 °C, indicative of ductile fracture. In addition, the impact wear performance of the steels displayed a trend of initially decreasing and subsequently increasing across the pressure range of 0–150 MPa. The wear resistance of samples prepared without pressure and at 30 MPa was superior to that at 60 MPa, and the wear resistance deteriorated when the pressure increased to 60 MPa, after which it exhibited an upward trend as the pressure continued to rise. The wear mechanisms of the samples predominantly consisted of impact wear, adhesive wear, and minimal abrasive wear, along with notable occurrences of plastic removal, furrows, and spalling.

The Influence of the Combined Addition of La–Ce Mixed Rare Earths and Sr on the Microstructure and Mechanical Properties of AlSi10MnMg Alloy

This study investigated the effect of adding La–Ce mixed rare earths and Sr on the microstructure and mechanical properties of AlSi10MnMg alloy. The experiment utilized different combinations of modifiers, including single La–Ce rare earths, single Sr, and the combined addition of La–Ce mixed rare earths and Sr. This study compared their effects on grain refinement, the modification of the α-Al phase and eutectic silicon phase, and tensile properties and hardness. The results showed that the combined modification of Sr and mixed rare earth elements significantly refined the grains, optimized the morphology of the α-Al phase and eutectic silicon phase, and improved the overall mechanical properties of the aluminum alloy. Under the combined modification, the addition of 0.02 wt.% Sr and 0.1 wt.% RE (La–Ce mixed rare earths) exhibited the most pronounced refining effect. The secondary dendrite arm spacing (SDAS) was reduced by 59.18%. The eutectic silicon phase transformed from coarse needle-like shapes to fine fibrous or granular forms, with an aspect ratio reduction of 69.39%. Meanwhile, the alloy’s tensile strength and hardness were significantly improved. The tensile strength increased to 240 MPa, achieving an increase of 23.08%; the yield strength increased to 111 MPa, achieving an increase of 18.09%; and the elongation reached 7.3%, achieving an increase of 73.81%. This indicates that the proper addition of Sr and mixed rare earths can significantly optimize the microstructure and enhance the mechanical properties of AlSi10MnMg alloy, providing an effective method for the preparation of high-performance heat-treatment-free aluminum alloys.

Experimental investigation on effect of cooling rate on carbide precipitation during solidification of high manganese steel

In order to elucidate the effect of cooling rate on the carbide formation during the solidification process of high manganese steel Mn13, the solidification process is artificially divided into two stages, namely the liquid-solid phase transition stage and solid-state cooling stage. The final Mn13 samples with different cooling rates are used to the analysis of solidification structure and carbides by high-temperature confocal microscopy (HTCLSM), optical microscopy (OM), electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM). The result shows that the change of cooling rate at the liquid-solid phase transition stage has a great influence on the solidification structure and carbide precipitation. At this stage, with the increase of cooling rate from 0.2 °C/s to 5.0 °C/s, the dendrite structure is obviously refined, and the secondary dendrite arm spacing and cooling rate are satisfied with the relationship: λΠ=54.14×v−0.33. Also, the average grain size in the Mn13 sample decreases from 549 μm to 346 μm, and the aspect ratio of gains in the Mn13 sample increases from 1.7 to 2.0. Moreover, the distribution of carbide in the interdendritic regions and grain boundaries increases, and the morphology of carbide at the grain boundary change from block to dendrite. But it seems that the change of cooling rate from 1 °C/s to 5.0 °C/s at the solid-state cooling stage has a slight effect on the secondary dendrite arm spacing, the average size and aspect ratio of the grain structure and the amount and morphology of carbide precipitation at the grain boundary.

Towards optimizing cooling rate, microstructure, and compressive strength in rapidly solidified Cu–20Fe alloy

There is currently interest in the development new Cu–Fe alloys with higher Fe content (>5 wt%), a low-cost element. In order to improve electrical, thermal and mechanical properties, there is a need to decrease the size of the Fe-rich phase and improve its distribution, whose possibilities rely on adding alloying third elements and heat treatments. However, the prospect of controlling the size of the phase through dendritic spacing control by means of rapid solidification processes may be feasible and deserves to be explored, as is the case in the present study. The following methods were employed to evaluate the round stepped cast samples of the Cu-20 wt% Fe alloy: centrifugal casting in a Cu mold, optical microscopy, CALPHAD, Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS), X-ray Diffraction (XRD), Vickers hardness, and compressive tests, in samples corresponding to different coarsening microstructures. Finally, dendritic growth is modelled using the Kirkwood equation. The results demonstrate a promising processing route with control of the secondary dendrite arm spacing (SDAS), whose methodology and modeling can serve as a basis for other alternative processes with the Cu–Fe alloys, allowing suitable size and distribution of Fe phase to be attained. It is further demonstrated that the Kirkwood model is able to match experimental SDAS in both slowly and rapidly solidified Cu–Fe samples. While Fe (BCC) is expected to increase strength, this is only slightly observed in the hardness results for smaller SDAS, as the loads are more superficial. In the case of compressive yield strength, SDAS in the observed range (1.4 μm–2.2 μm) is found to have no effect.

Solidification of Tungsten Inert Gas–Welded Austenitic Stainless Steel with 0.17 wt% N

In this study, an austenitic CrMnNi–N steel is examined with regard to its solidification behavior of the weld metal. For this purpose, the cooling rate of the weld metal at different welding speeds is determined for tungsten inert gas welding without filler metal. The relationship between secondary dendrite arm spacing () and cooling rate () can be described using . Moreover, the microstructure is characterized by a scanning electron microscope using energy‐dispersive X‐ray spectroscopy (EDS). Based on the EDS measurement, it is possible to describe the microsegregation of Cr, Ni, Mn, Mo, and N. The detected microsegregation behavior is compared with the results obtained from Thermo‐Calc calculations. The microsegregation varies depending on the present phase during solidification and correlate well with microstructure observations. By using the software Thermo‐Calc, the theoretical description of solidification is based on the classical Scheil model with fast diffusion of N. A primary ferritic solidification is calculated, which correlates with the experimental findings.

Effect of cooling rate on solidification microstructure, microsegregation, and nanoprecipitates in medium carbon CrMo cast steel

Precipitation strengthening is a crucial method for enhancing the mechanical properties of steel. The bridgman directional solidification furnace, optical microscope (OM), scanning electron microscope (SEM), electron probe analyzer (EPMA) and transmission electron microscope (TEM) were used to investigate the effect of solidification cooling rate on the solidification microstructure, microsegregation, and nanoprecipitates in medium carbon CrMo cast steel. The results indicate that as the cooling rate increases, the solidification microstructure is significantly refined. The relationship between the cooling rate (CA) and primary dendrite arm spacing (PDAS, λ1) and secondary dendrite arm spacing (SDAS, λ2) are given by λ1 = 123.74 × C-0.4088A, λ2 = 66.63 × C-0.6532A. Solute elements like Cr, Mo, and V exhibit noticeable positive segregation in the inter-dendritic. When the cooling rate does not exceed 0.47 °C/s, the solute concentrations in the inter-dendritic increase with higher cooling rate, leading to a decrease in the effective solute partition coefficient. This phenomenon is primarily attributed to the back diffusion of solute elements during solidification. Following heat treatment, precipitation of M6C, V(C,N), and M23C6 occurs within the inter-dendritic regions. If the solidification cooling rate does not exceed 0.47 °C/s, the density and volume fraction of nanoprecipitates increase with higher cooling rate. This trend primarily results from the reduction in critical nucleation radius and critical nucleation energy, facilitating easier nucleation of nanoprecipitates.

Effect of cladding speed on the microstructure and hardness of high-hardness B-bearing Cr17Ni2 coating

The B-bearing iron-based coating produced by laser cladding exhibits super-high hardness. However, the strengthening mechanism of B-bearing Cr17Ni2 coating and non-equilibrium phase transformation during the cooling stage require further investigation. The study focused on the B-bearing Cr17Ni2 coatings produced by laser cladding at four speeds ranging from 10 mm/s to 200 mm/s. The results show that the thickness of the single layer in the coatings gradually decrease as the increase of scanning speed. The secondary dendrite arms spacing and grain size also decrease with increasing scanning speed. The microstructure of the coating consists of a martensitic phase and a eutectic phase consisting of Cr2B compounds and austenite. Combined with G\\R diagram and finite element analysis, the microstructure refining mechanism of the coating has been concluded. The effect of fine grain strengthening, solid solution strengthening, precipitation strengthening, and dislocation strengthening on hardness is investigated. It has been observed that the coating hardness increases with increasing scanning speed. This change in the hardness of the coatings is mainly because of the grain and precipitate refining.

Study on the characteristics and high-temperature dissolution mechanism of eutectic carbides in medium-alloy steel

In this study, the high-temperature evolution of eutectic carbides in a medium-alloy steel was investigated as well as their precipitation mechanism. Results revealed that MC and M6C eutectic carbides in the steel appeared during the final solidification due to the segregation of Mo and V and the melt undercooling. These eutectic carbides consist of blocky shapes with varying orientations, and rod-like shapes with the same orientation. Further investigation was confirmed that the carbides (MC and M6C) exhibited an intergrowth behavior. The cooling rate had a direct influence on the secondary dendrite arm spacing (SDAS), which decreased from 180 to 130 μm as the rate ranged from 0.6 to 21.9 °C/min. After holding for 0, 25, 50, and 80 h, respectively, the volume percentage of eutectic carbides exhibited a significant decreasing trend from 2 to 0.2%. Additionaly, the carbides exhibited irregular morphology after holding for 0–50 h, respectively, and which was transformed into the rod-like shape with a small size distributed along the grain boundaries after holding for 80 h. This phenomenon was attributed to the mutual diffusion between Mo, V, and other alloying elements in the carbides and Fe element in the steel matrix.

Impact of Aging Time on the Metallurgical Properties and Hardness Characteristics of an Al-Si-Mg-Cr Hypoeutectic Alloy Intended for Automotive Applications

This research investigates the microstructural evolution and mechanical properties of LM25 (Al-Si-Mg) alloy and Cr-modified LM25-Cr (Al-Si-Mg-Cr) alloy. Microstructural analysis reveals distinctive ε-Si phase morphologies, with Cr addition refining dendritic structures and reducing secondary dendrite arm spacing in the as-cast condition. Cr modification results in smaller-sized grains and a modified ε-Si phase, enhancing nucleation sites and reducing ε-Si size. Microhardness studies demonstrate significant increases in hardness for both alloys after solutionising and aging treatments. Cr-enriched alloy exhibits superior hardness due to solid solution strengthening, and prolonged aging further influences ε-Si particle size and distribution. The concurrent rise in microhardness, attributed to refined dendritic structures and unique ε-Si morphology, underscores the crucial role of Cr modification in tailoring the mechanical properties of aluminium alloys for specific applications.

Carbon Macrosegregation Pattern in 30Cr15Mo1N Ingot: Impact of Pouring Rate

The effect of the pouring rate on the carbon macrosegregation in 30Cr15Mo1N ingots has been clarified by investigating changes in the content of carbon‐containing precipitated phases, cooling rate, secondary dendrite arm spacing (SDAS) and the flow characteristics of molten steel. During the solidification process, the solute‐enriched liquid steel migrates toward the center of the ingot under the action of convection, resulting in an increasing segregation ratio from the edge to the center. However, the growth of equiaxed grains partially restricts the flow of solute‐enriched liquid steel, which leads to a maximum segregation ratio not at the center but at approximately a quarter radius from the center. Furthermore, due to the upward flow of molten steel in the center, positive segregation occurs at the top. An increment in the pouring rate reduces the SDAS by enhancing the cooling rate, and thus the permeability decreases. It aggravates the carbon macrosegregation horizontally. However, increasing the pouring rate decreases the carbon macrosegregation vertically. This is due to the more intense flow of molten steel and the larger liquid phase region at higher pouring rate, which reduces the solute enrichment degree and promotes compositional homogeneity above and below the ingot.

Microstructure and Tensile Properties of Ni-Base Superalloy IN738LC according to Solidification Rate and Heat Treatment

The strength of Ni-base superalloys mainly depends on the γ' precipitates that improve the strength of the materials at high temperatures. The presence of γ' particles within the matrix restricts dislocation movement, and optimized heat treatments can tailor the size, shape, and volume fraction of γ'. In this study the effects of solidification rate and solution temperature on the tensile properties of IN738LC superalloy were investigated. The secondary dendritic arm spacing of casting materials with different diameters was measured and the solidification rate of the casting materials was derived by comparing the results of the solidification microstructure obtained from a directional solidification experiment. The D17 material, which had a faster solidification rate, showed higher values of tensile strength and yield strength than the D60 material, which had a slower solidification rate. The study also concluded that the monomodal γ' precipitates in the S80 material have higher tensile strength and yield strength at room temperature and 760℃ than the bimodal γ' precipitates in the S20 material. As for the deformation behavior at 760℃, an isolated stacking fault was observed in the S20 material only within the large γ’ precipitates. In the S80 material, the high dislocation density increased the yield strength due to the strong interaction between dislocations and fine γ’ precipitates.

Predicting the effect of cooling rates and initial hydrogen concentrations on porosity formation in Al‐Si castings

AbstractAl‐Si alloys are widely used in automotive casting components while microporosity has always been a detrimental defect that leads to property degradation. In this study, a coupled three‐dimensional cellular automata (CA) model has been used to predict the hydrogen porosity as functions of cooling rate and initial hydrogen concentration. By quantifying the pore characteristics, it has been found that the average equivalent pore diameter decreases from 40.43 to 23.98 μm and the pore number density increases from 10.3 to 26.6 mm−3 as the cooling rate changes from 2.6 to 19.4°C/s at the initial hydrogen concentration of 0.25 mL/100 g. It is also notable that the pore size increases as the initial hydrogen concentration changes from 0.15 to 0.25 mL/100 g while the pore number remains stable. In addition, the linear regression between secondary dendrite arm spacing and the equivalent pore diameter has been studied for the first time, matching well with experiments. This work exhibits the application of CA model in future process optimization and robust condition design for advanced automotive parts made of Al‐Si alloys.

A Numerical Time Integration Procedure for Secondary Dendrite Arm Spacing in Hyper-Peritectic Steel Alloys

AbstractA numerical time integration procedure for the calculation of the secondary dendrite arm spacing (SDAS) in FeC hyper-peritectic alloys is presented, a preferred group of low-carbon casting steel. The procedure incorporates a three-stage thin arm dissolution model, which is solved at each time step using Newton–Raphson iteration. This is coupled to a coarsening model based on the integral forms of the dissolution model, which are solved using Gaussian quadrature, as well as a growth model for solid fraction evolution. The procedure can easily be embedded into numerical models for solidification, in which the space–time evolution of the SDAS is required for determining the dynamic permeability in the mushy zone. Higher order approximations for both growth and solute concentration evolution can easily be incorporated. Temperature dependence of thermophysical parameters is taken into account using inter-dendritic solidification empirical models, and an alloy-specific peritectic reaction constant is used to determine the isothermal peritectic holding time. The procedure is validated against experimental data presented in literature. Various cases of SDAS as a function of local solidification time, cooling rate and carbon composition are investigated. The method is compared to experimental results of SDAS obtained from test castings of a hyper-peritectic steel alloy and can be used to iteratively determine the alloy-specific peritectic reaction constant by comparing the solid fraction evolution during the peritectic reaction with that found from the experimental cooling curve.

Joint Characteristics of Cu-Ni Alloy Fabricated by GTAW and MPAW Processes: A Comparative Study

The current work presents a comparative analysis of the joint behavior of Cu-Ni alloy weldments fabricated by Micro-Plasma Arc Welding (MPAW) and Gas Tungsten Arc Welding (GTAW) processes. The Cu-Ni alloy thin sheets are fabricated at different values of heat input (~40-135 J/mm) by MPAW and GTAW processes, respectively. Further, to evaluate their characteristics, joints are subjected to metallurgical, mechanical, and electrochemical testing. The joints fabricated with a higher magnitude of heat input resulted in deteriorated surface quality with a value of Ra~ 6.13 μm. The increased surface roughness value of the joints resulted in a higher corrosion rate (1.273 mm/year). A finer microstructural morphology is achieved for lower heat input condition. Accordingly, the weldment exhibited higher joint efficiency of ~91%.The prominent reason for achieving higher joint strength is related to the presence of lower secondary dendritic arm spacing (SDAS), which enhances the joint strength and ductility for the joints as compared to higher SDAS value. Further, the micro-fractography analysis reveals the presence of micro/macro-voids for high heat input, whereas the existence of numerous dimples of varying size and depth is observed for low heat input condition, implying the role of heat input of utmost importance.