Columnar Dendrites Research Articles

Hardening Mechanism of Thick (Ti,Cr,V)N Composite Coatings with Multi-layer Nano-columnar Dendrites Microstructure

The 300 μm thick (Ti,Cr,V)N nanocomposite coatings were prepared by plasma spraying technique combined with combustion synthesis reaction of N and Ti-Cr-V reconstituted composite powders, and their microstructure and hardening mechanism were explored. The phases and microstructures were analysed by X-ray diffractometer, X-ray photoelectron spectroscopy and scanning electron microscopy, transmission electron microscopy, respectively, and a microhardness tester was employed to measure the microhardness. The main phase of the composite coating is (Ti,Cr,V)N solid solution, which has a multilayered structure of elongated columnar dendrites arranged in parallel, with different solidification positions resulting in crystal bundles possibly having different orientations. The composite coating has nanoscale fine crystals, as well as two typical strengthening models, "dislocation-TB" and "lattice distortion", which together contribute to the high hardness of the (Ti,Cr,V)N composite coating. The (Ti,Cr,V)N composite coating containing 10wt.% Cr has better surface morphology and the highest microhardness value (1844.80 HV0.5).

Microstructural Inhomogeneity in the Fusion Zone of Laser Welds.

This paper investigated evolutions of α-Al sub-grains' morphology and crystalline orientation in the fusion zone during laser welding of 2A12 aluminum alloys. Based on this, a new method for assessing the weldability of materials was proposed. In laser deep-penetration welding, in addition to the conventional columnar and equiaxed dendrites, there also exhibited a corrugated structure with several 'fine-coarse-fine' transformations. In such regions, an abnormal α-Al coarsening phenomenon was encountered, with a more dispersed crystalline orientation arrangement and a decreased maximum pole density value. Particularly, structural alterations appeared more frequently in the weld bottom than the top. The above results indicated that the laser-induced keyhole presented a continually fluctuating state. Under such a condition, the solid-liquid transformation exhibited an unstable solidification front, a fluctuant undercooling, and a variational solidification rate. Meanwhile, the welding quality of this material is in a critical state to generate pores. Therefore, the appearance and relevant number of corrugated regions can be considered as a new way for judging the weldability, which will help to narrow the processing window with better welding stability.

Building ultra-thin Inconel 718 sheet joints using low-frequency PLBW scheme: Weld bead quality, keyhole dynamics, and solidification characteristics

Low-frequency pulsed laser beam welding (PLBW) was employed in building 0.32 mm-thick Inconel 718 superalloy butt joints which are frequently applied in manufacturing high-temperature functional units in the aviation industry. Several process parameter combinations concerning peak laser power, welding speed, and pulse frequency were implemented to explore the macro morphology, microstructure, and mechanical properties of the welded joints. Examinations exhibit that the resulting weld beads possess high continuity at the surface with an overlap factor ranging from 0.58 to 0.73. The cross-sectional profile changes from a V-shape to an H-shape with increasing heat input. Finer grain structures composed of γ matrix and γ/Laves eutectic penetration are observed within the FZ center, as compared to that near the fusion line. Excellent performance is achieved in microhardness and tensile tests. Numerical simulation based on an integrated mathematic model reveals periodic keyhole and weld pool dynamics depending on the pulsing laser power. During a typical pulse interval, keyhole geometry collapses within a fraction of a millisecond, leading to a sharp cooling stage at ∼4 × 106 K/s, and then, the melt cools due to the thermal convection with a normal cooling rate of 105 K/s. The full growth of the adjacent weld spot results in the secondary melting zone (SMZ), wherein the columnar dendrites can be refined mainly due to the heterogeneous nucleation as compared to the primary melting zone (PMZ).

The morphology features, formation mechanism and elimination of channel segregation in industrial-scale Ti–Nb ingots produced by vacuum arc remelting

In this study, the morphology characteristics and formation mechanism of channel segregation in the industrial-sized Ti–Nb binary ingots produced by vacuum arc remelting (VAR) are researched based on experiments and calculations. The results show that the channel segregation is usually located at the 1/4–3/4 radius of the ingot and the morphology is closely related to the VAR process. The Ti-enriched channel segregation stripes tend to parallel to the ingot centerline and columnar dendrites in steady-state remelting region and hot-top region, respectively, while along the molten pool profile in residual molten pool region. For the first time, the Ti2O3 particles precipitated in the channel segregation were observed, following the orientation relationship of <001>β//<133>Ti2O3 and {11‾0}β//{011‾}Ti2O3 with β matrix in coherent boundary. First-principles calculations evident that the enrichment of Ti-solute tends to decrease the formation enthalpy, and hence makes for the precipitation of Ti2O3 particles. The numerical simulation and the experiment results manifest that the channel segregation originates from the convergence of interdendritic Ti-enriched liquid, resulting in the density inversion between the Ti-enriched initiation site and the surrounding liquid. The density gradient and the solidification rate dominate the growth direction and the radius distribution of the channel segregation. Based on the above, an optimized technique with helium cooling and the external stirring magnetic field was conducted and the channel segregation was eliminated successfully.

Nd: YAG laser beam welding of UNS N07718 superalloy and UNS S32304 duplex stainless steel: Phase transformations and mechanical properties of dissimilar joints

This article implies the phase transformations and mechanical behavior of dissimilar laser welded UNS N07718 superalloy/UNS S32304 duplex stainless steel. Laser power, welding speed, and focal point were the variables of the laser beam welding (LBW) approach. Optical microscopy and electron backscattered diffraction (EBSD) analysis were utilized. They demonstrated that the weld metal (WM) mainly had an austenitic microstructure with a face-centered cubic structure in the form of columnar and equiaxed dendrites. Also, the occurrence of directional solidification in WM was verified by EBSD. The heat-affected zone (HAZ) microstructure of Inconel 718 superalloy included austenite grains with normal grain growth, annealing twins, and precipitates. There was a ferritic-austenitic microstructure in the HAZ of 2304 duplex stainless. In this area, the volume fraction of the ferrite phase was excessively higher than that of the austenite phase and the austenite was characterized as Widmanstätten plates and grain boundary austenite. Furthermore, abnormal ferrite grain growth was identified in this. Welding defects e.g., molten spatter, solidification crack, and lack of penetration were observed, as well. Based on the uniaxial tensile test, it was realized that the highest failure load (9.7 ± 0.4 kN) was achieved in the laser power of 1900 W, welding speed of 3 mm/s, and focal point of 0 mm. Therefore, these variables were known as the optimum variables of the LBW process. All laser weldments failed from the WM and fractography via scanning electron microscopy (SEM) showed a mixture of dimple and cleavage features in the fracture surfaces of the laser welds.

Interaction between growing dendrite and rising bubble under convection

Prediction and control of gas porosity defect during solidification is challenging because of multiphase and multiphysics characteristics. In this work, a multiphase-field lattice Boltzmann method is employed to study the interaction between solidifying dendrite and rising bubble. The influencing factors are divided into two categories including external and internal factors, and the effects of the multiple factors are discussed and compared. The bubble changes the dendrite skeleton by hindering the solid growth, including entrapped in the dendrite root, tilting growth towards the neighboring bubble, forming the knot structure, and growing along the radial direction of the bubble. The bubble in the columnar dendrite array with random orientation distribution has larger effects on the average primary dendrite arm spacing. Based on the summary of different interaction results, a phase diagram is proposed to distinguish different interaction regimes. Further, the size of the closed liquid phase region is measured to evaluate the porosities tendency and guide how to reduce the porosities.

Effect of laser power on microstructure and mechanical properties of K418 nickel-based alloy prepared by selective laser melting

K418 alloy was prepared by selective laser melting (SLM) at different laser powers (160∼240 W) in this paper. The influence of laser power on the densification behavior, microstructure, microhardness, and tensile properties was studied systematically. The results showed that the densities of the material increased rapidly first and then decreased slowly with the increase of laser power. When the laser power increased from 160 W to 240 W, the surface defects of the specimen decreased, the microstructure changed from columnar dendrites to cellular, and the grains grew in the <001> direction preferentially. When the laser power is 200 W, the grain size is the smallest, the content of small-angle grain boundaries is more, the Schmidt factor is less, and then the best mechanical properties are achieved, at which the microhardness reaches 362.89 ± 5.01 HV, the tensile strength reaches 1244.35 ± 70.1 MPa, the yield strength reaches 863.89 ± 23.1 MPa, and the elongation of the material reaches a maximum of 12.53 ± 0.71 %. In addition, the fracture mode of the material is a mixed tough-brittle fracture mechanism.

Optimizing solidification dendrites and process parameters for laser powder bed fusion additive manufacturing of GH3536 superalloy by finite volume and phase-field method

Investigating the surface morphology and microstructure of laser powder bed fusion (L-PBF) in solidification and optimizing process parameters is crucial for improving the accuracy and performance of cladding parts of GH3536 superalloy. In this study, a computational model incorporating Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) was utilized to simulate the mesoscale evolution of the molten pool in L-PBF for GH3536 superalloy. Furthermore, the growth of columnar dendrites along the fusion boundary under transient conditions was simulated utilizing a quantitative phase-field model. The impact of scanning speed and laser power on temperature distribution, molten pool size, surface morphology of cladding layer, and columnar dendrite spacing during solidification of single-track L-PBF were examined. The findings suggest that the molten pool undergoes a fast process characterized by significant temperature gradients. Increasing the laser power or reducing the scanning speed results in higher maximum molten pool temperature, as well as increased molten pool depth and width. Overlarge or undersized scanning speed and laser power can result in poor surface quality of the cladding layer. When the laser power was 120 W and the scan speed was 0.4 m/s, the cladding layer exhibited improved surface morphology, with finer columnar dendrites observed at the molten pool's base. This study delved into understanding the evolution characteristics of the molten pool and the growth process of columnar dendrites at the molten pool's base, providing valuable insights for determining appropriate experimental process parameters for L-PBF of GH3536 superalloy.

Twinned dendrites in TiAl alloys

A novel dendrite splitting phenomenon in as-cast TiAl alloys was observed to show microstructural morphologies as well as crystallographic characteristics similar to those of twinned dendrites. For a β-solidified TiAl alloy, the solidified dendrite is splitted in the center by a {111} plane, the parts on both sides of which follow a particular orientation relationship that resembles twinned dendrites in Al alloys. In other words, the dendrite splitting yields twinned dendrite. The formation mechanism of twinned dendrites is related to the atom attachment behaviors at the liquid-solid interface during solidification. For the TiAl alloy with the primary phase being γ, straight twinned {111} plane layers with the thickness of a few to dozens of microns form longitudinally in the center of the columnar dendrites. The same orientation relationships appear in both β- and γ-solidified TiAl alloys, although their primary phases are different. This paper provides new details involved in the solidification of TiAl alloys.

Oscillating energy deposition of 17-4 PH alloy reinforced with tungsten carbide particles

17-4 PH is a martensitic precipitation-hardening stainless steel, renowned for its exceptional strength and high-temperature resistance, making it extensively employed in the fabrication of aircraft engines and flight control systems. The strengthening method of this alloy involves precipitation strengthening through thermal treatment. However, it is also susceptible to grain growth, which can diminish the alloy's mechanical properties and corrosion resistance. This research proposes to use circular oscillating laser deposition of 17-4 PH alloy reinforced with tungsten carbide (WC) and compares it with Gaussian laser deposition. The research findings indicate that the circular oscillating laser induces a stirring effect on the molten pool, facilitating the transformation of columnar dendrites into equiaxed grains and thereby refining the grain size. The convection, intensified by the high temperature and stirring effect, promotes the melting and diffusion of WC particles. The reaction between W, C elements, and 17-4 PH alloy facilitates the precipitation of hard phase carbides. Compared to Gaussian laser deposition, the microhardness of the 7 wt% WC/17-4 PH material prepared by circular oscillating laser deposition increased by 21.25 %, and the wear rate decreased by 70.06 %. The electrochemical test results have revealed that the 7 wt%WC/17-4 PH composite material fabricated using Gaussian laser exhibits optimal corrosion resistance. The circular oscillating laser induces carbide deposition at grain boundaries, resulting in the formation of microcells and exacerbating the corrosion.

Functionally graded deposition of dissimilar steel (316LSi and ER70S-6) fabricated through twin-wire arc additive manufacturing

Fabrication of dissimilar steel-based (SS316LSi over ER70S-6 steel) functionally graded deposition (FGD) using twin wire arc additive manufacturing (T-WAAM) via a unique deposition strategy is investigated in this work. Optical, SEM, EDS, X-ray diffraction (XRD), tensile, hardness, and fractography analyses were undertaken for complete microstructural and mechanical characterisation. Microstructural analysis revealed columnar, equiaxed, and cellular dendrites in δ-ferrite and austenitic phases. XRD investigation depicted the anisotropic behaviour of specimen textures in various planes. The estimated value of average ultimate tensile strength is 901 MPa, yield strength (YS) is 634 MPa, and percentage elongation (EL%) is 48 %, respectively. This work offers a novel strategy for producing superior-strength dissimilar steel components with excellent quality and varied structural utility.

Improving the deposition efficiency and mechanical properties of additive manufactured Inconel 625 through hot wire laser metal deposition

This study focuses on the advantages of hot wire laser metal deposition (HW-LMD) compared to cold wire deposition technology (CW-LMD) for fabricating Inconel 625 alloy. Initially, a comparative study was conducted through single-pass deposition experiments to evaluate the process characteristics of HW-LMD and CW-LMD. The results showed that by increasing the additional resistance heat by 20% during HW-LMD, a significant 92.5% increase in wire deposition rate and a 60.3% increase in energy efficiency were achieved. Additionally, the wire deposition rate of HW-LMD was 1.5 times as high as that of CW-LMD with the identical total energy input. Subsequently, well-formed Inconel 625 bulks were fabricated using both CW-LMD and HW-LMD techniques. The microstructures and mechanical properties of the as-deposited samples manufactured by the two different processes were comparatively studied. Due to the accelerated solidification rate of the molten pool, the columnar dendrites in Inconel 625 samples prepared by HW-LMD were refined, resulting in an average grain size of 12 µm. Furthermore, the precipitation of the Laves phase at the inter-dendrite regions was suppressed. Consequently, an increased microhardness of 258 HV1.0 for HW-LMD samples was obtained. In addition, the HW-LMD samples also exhibited superior tensile strength and elongation, measuring at 837.4 MPa and 55.2% respectively. Based on the aforementioned findings, HW-LMD has demonstrated outstanding capability in improving productivity and mechanical properties, indicating a promising option for efficient additive repair and manufacturing.

Formation of eutectic structure and de/ hydriding kinetics properties: A novel Ti-Hf-V-Mn multi-principal element alloy

The novel Ti23-xV40Mn37Hfx (x = 8 and 10 at%) multi-principal element alloys (MPEAs) were prepared using vacuum non-consumable electrode arc-melting furnace. An analysis of the hydrogen sorption process unveiled a thought-provoking discovery, shedding light on the microstructure and performance of the alloys. The MPEAs exhibited a higher abundance of the C14 Laves phase in comparison to the Ti23V40Mn37 alloy. The C14 Laves phase underwent a transformation into columnar dendrites, resulting in the formation of a finely textured eutectic structure within the MPEAs. This distinctive microstructure endowed the MPEAs with superior activity and faster hydrogen absorption kinetics compared to the Ti23V40Mn37 alloy. The initial hydrogen absorption process followed a nucleation and crystal growth mechanism. In addition, the Ti13V40Mn37Hf10 alloy exhibited an impressive maximum hydrogen desorption capacity of 1.96 wt%, representing a significant 38% increase when compared to the Ti23V40Mn37 alloy. This enhanced hydrogen desorption capacity can be attributed to the presence of numerous diffusion channels for hydrogen atoms, as well as shorter diffusion distances within the MPEAs. Furthermore, the values of ΔH increased to 30.38 and 32.76 kJ/mol H2, respectively, for the MPEAs. This indicates a higher stability of hydrides within the MPEAs.

Development of a bilayer NiCrAlY/YSZ coating on IN713 LC superalloy by laser cladding

In this study, bilayer laser cladding of Inconel 713LC superalloy was performed by a Nd:YAG laser. Amdry 997 powder was used as the first layer and Metco 204NS ceramic powder as the second layer. The experiments were carried out with different laser parameters to investigate the influence of heat input and laser power density on the microstructure and the hardness of coating. The study revealed that the susceptibility to crack formation in the clad zone increases with the increase in the heat input due to the high cooling rate and intense thermal stress. The formation of shrinkage cavities in the lower half of the clad zone raises with the increase in the heat input owing to reduction in the solidification rate. Microstructural investigations show that a cellular structure is formed at the interface region. The middle area of coating features columnar dendrites, while the upper area of the coating displays very small equiaxed dendrites. The coating mainly comprises γ-Ni, β-NiAl and γ′-Ni3Al phases and the elements of Ni, Co, Cr, Al, Ta, Zr, and Y are homogeneously distributed in the clad zone. As the heat input increases, the microhardness of the samples decreases due to an increase in the dilution ratio. This leads to a decrease of Co, Cr, and Ta elements in the γ′ and the β intermetallic compounds, as well as a reduction of Zr and Y elements in the clad zone.

Hot-Cracking Mechanism of Laser Welding of Aluminum Alloy 6061 in Lap Joint Configuration.

Laser welding, known for its distinctive advantages, has become significantly valuable in the automotive industry. However, in this context, the frequent occurrence of hot cracking necessitates further investigation into this phenomenon. This research aims to understand the hot-cracking mechanism in aluminum alloy (AA) 6061, welded using a laser beam in a lap joint setup. We used an array of material characterization methods to study the effects of processing parameters on the cracking susceptibility and to elucidate the hot-cracking mechanism. A laser power of 2000 W generated large hot cracks crossing the whole weld zone for all welding speed conditions. Our findings suggest that using a heat input of 30 J/mm significantly mitigates the likelihood of hot cracking. Furthermore, we observed that the concentrations of the alloying elements in the cracked region markedly surpassed the tolerable limits of some elements (silicon: 2.3 times, chromium: 8.1 times, and iron: 2.7 times, on average) in AA6061. The hot-cracking mechanism shows that the crack initiates from the weld root at the interface between the two welded plates and then extends along the columnar dendrite growth direction. Once the crack reaches the central region of the fusion zone, it veers upward, following the cooling direction in this area. Our comprehensive investigation indicates that the onset and propagation of hot cracks are influenced by a combination of factors, such as stress, strain, and the concentration of alloying elements within the intergranular region.

Optimum process parameters of IN718 alloy fabricated by plasma arc additive manufacturing using Taguchi-based grey relational analysis

The process parameters of IN718 alloy fabricated by plasma arc additive manufacturing (PAAM) were evaluated by Taguchi-based grey relational analysis, and the microstructure and mechanical properties of the PAAM alloy were analyzed to verify the optimized process parameters. The results show that the influence of each process parameter on the dilution ratio and forming coefficient is consistent. Based on the results of Taguchi-based grey relational analysis, the optimized process parameters for PAAM IN718 alloy are plasma arc current 115 A, scanning rate 1000 mm/min, powder feeding rate 16 g/min, and shielding gas flow 800 L/h. The plasma arc current and powder feeding rate play primary roles in the dilution rate and forming coefficient of PAAM IN718 alloy. With the optimized process parameters, the forming and internal crack of the PAAM IN718 alloy is controlled. The microstructure of PAAM IN718 alloy is dominated by temperature gradient and constitutional supercooling, which is sequentially transformed from cellular crystal in the bottom region to coarse columnar dendrite and equiaxed crystal in the top region. Laves phase exhibits a concentration gradient that gradually increases from top to bottom on the cross-section from the range 11.3–18.6 vol%. Due to the solid solution strengthening of Nb/Mo elements and dispersion strengthening by γ″ phase, the microhardness and tensile strength of PAAM alloy after full heat treatment reach about 500 HV and 1284 MPa, respectively. These are satisfactory mechanical properties compared to other additive manufactured IN718 alloys, and PAAM is suitable to prepare IN718 alloy to obtain favorable microstructure and mechanical properties.

Effect mechanism of arc oscillation on microstructure and mechanical performance of SUS304 weld seams manufactured by local dry underwater double pulsed MIG welding

An innovative local dry underwater double pulsed MIG (LDU-DPMIG) technique was successfully applied to fabricate SUS304 weld seams, in which the stirring effect on the molten pool was realized via a double pulsed current waveform. The weld formation, phase morphology and distribution, grain structure characteristics, microhardness, and tensile properties of underwater weld seams were comprehensively analyzed in this study, especially the mechanism differences between local dry underwater single pulsed MIG (LDU-SPMIG) and LDU-DPMIG were revealed. The results demonstrated that the stirring effect caused by arc oscillation contributed to the enhancement of the molten pool fluidity during the solidification process, which effectively facilitated the smooth elements allocations between austenite and ferrite and the evolution of δ-ferrite phase structure from skeleton to lath. In addition, the grain structure in the DPMIG weld centre transformed from slender columnar dendrites to fine equiaxed dendrites. Due to the pronounced stirring effects in uniform composition distribution, ferrite morphology evolution, grain refinement, and increased twin activity, DPMIG weld seams exhibited an attractive enhancement in weld mechanical performances, with the optimal low frequency of 3 Hz, the average microhardness, ultimate tensile strength, and elongation enhanced by the highest 18.1%, 8.9%, and 16.3% compared with SPMIG weld seam. These results are expected to offer a novel approach to regulate and control the microstructure and mechanical performance of underwater weld seams and facilitate the application of LDU-DPMIG in ocean engineering equipment.

An Analysis of the Mapping Relationship between Microstructure and Solidification Parameters during Aluminum Fused Coating

Metal fused-coating technology has the advantages of both low cost and high efficiency and is a new additive manufacturing technology in recent years. The previous studies were mainly aimed at the optimization of process parameters and the control of the surface quality of parts, while there were few theoretical analyses on the microstructure morphology after solidification. A three-dimensional transient numerical model was established to calculate temperature gradient and solidification rate, considering the changes in material physical properties with temperature during the calculation process. The temperature gradient on the substrate surface is jointly affected by the melt flowing out of the nozzle and the welding arc. It was found that the solidification front of the aluminum alloy was in an unstable state during the coating process. When the value of G/R decreases, the microstructure of the solidification interface gradually changes from columnar crystals to columnar dendrites and equiaxial crystals. The microstructure at the bottom of both the molten pool and coating layer is columnar crystal, while the microstructure at the upper part is equiaxed crystal.

Heterostructure microstructure and laves phase evolution mechanisms during inter-layer hammering hybrid directed energy deposition (DED) process

Directed energy deposition (DED) is suitable for fabrication of large Inconel 718 components, however, large columnar dendrites and several laves phase impair the mechanical properties. In this work, the formation mechanism of heterostructure microstructure with coarse grain (CG) and fine grain (FG) alternating distribution was explored, and the evolution process of Laves phase during inter-layer hammering hybrid directed energy deposition (HDED) was revealed. The results show that the heterostructure microstructure composed of CG region and FG region with a ratio of 1:1 was obtained due to the work hardening and recrystallization mechanisms, and the average grain size of CG region and FG region are 68.9 μm and 12.0 μm, respectively. The Laves phase was first fractured into small pieces by hammering and then resolved into the matrix during the subsequent heat input process, which promotes the precipitation of γ″ phase from the matrix. The strength and plasticity of the specimens fabricated by HDED are synchronously improved. The dislocation strengthening and solid solution strengthening are the mainly contributions to the strength improvement, and the grain refinement and heterostructure microstructure increased the plasticity of the hybrid manufactured specimens.

Dissimilar autogenous TIG joint of Alloy 617 and AISI 304H steel for AUSC application

To reduce costs and improve high-temperature performance in Advanced Ultra Super Critical (AUSC) boilers, it is necessary to weld austenitic steel to Inconel alloy. In this study, the autogenous tungsten inert gas (TIG) welding process was used to join Alloy 617 and an austenitic AISI 304H steel plate of thickness 5 mm. Microstructural analysis showed that the microstructure formation was uneven along the weldments, with columnar and cellular dendrites near the interface while the central area of the weld exhibited a combination of columnar, cellular, and equiaxed dendrites. The use of energy dispersive spectroscopy and electron probe micro-analysis unveiled the presence of an unmixed layer at the interface between the weld and AISI 304H steel. Furthermore, a notable variation in the concentration of alloying elements such as Fe, Cr, Ni, Co, and Mo was observed. Within the weld metal, inter-dendritic areas showed the presence of precipitates rich in Cr, Ti, and Mo. Meanwhile, the heat-affected zone (HAZ) of Alloy 617 exhibited the presence of phases like Cr and Mo-rich M23C6 as well as Mo-rich M6C. Hardness tests showed non-uniform hardness along the weldments, with a hardness of 199 ± 6 HV in the weld metal and 225 ± 4 HV in Alloy 617 HAZ, and 207 ± 7 HV in AISI 304H HAZ. The Mo and Cr segregation in the inter-dendritic spaces led to a decline in the tensile properties of the welded parts and resulted in failure from the region of the weld metal.