Showing papers on "Liquation published in 2007"

Effect of heat input on heat affected zone cracking in laser welded ATI Allvac 718Plus superalloy

Abstract: The heat affected zones (HAZs) of low and high heat input laser welds of a newly developed superalloy, ATI Allvac 718Plus, were studied. Low heat input welds suffered significant HAZ grain boundary liquation cracking, while no cracking was observed in spite of a more extensive HAZ intergranular liquation in the higher heat input welds. Combination of lower welding stresses generated during cooling, and relaxation of these stresses by thick intergranular liquid were suggested to be the factors that contributed to the absence of cracking in the high heat input welds. Further, healing of some of the HAZ cracks in lower heat input welds by fusion zone interdendritic liquid occurred through liquid backfilling.

Liquation Microfissuring in the Weld Heat-Affected Zone of an Overaged Precipitation-Hardened Nickel-Base Superalloy

Abstract: The effect of preweld overaging heat treatment on the microstructural response in the heat-affected zone (HAZ) of a precipitation-hardened nickel-base superalloy INCONEL 738LC subjected to the welding thermal cycle (i.e., rapid) was investigated. The overaging heat treatment resulted in the formation of an interfacial microconstituent containing M23X6 particles and coarsening of primary and secondary γ′ precipitates. The HAZ microstructures around welds in the overaged alloy were simulated using the Gleeble thermomechanical simulation system. Microstructural examination of simulated HAZs and those present in tungsten inert gas (TIG) welded specimens showed the occurrence of extensive grain boundary liquation involving liquation reaction of the interfacial microconstituents containing M23X6 particles and MC-type carbides. In addition, the coarsened γ′ precipitate particles present in the overaged alloy persisted well above their solvus temperature to temperatures where they constitutionally liquated and contributed to considerable liquation of grain boundaries, during continuous rapid heating. Intergranular HAZ microfissuring, with resolidified product formed mostly on one side of the microfissures, was observed in welded specimens. This suggested that the HAZ microfissuring generally occurred by decohesion across one of the solid-liquid interfaces during the grain boundary liquation stage of the weld thermal cycle. Correlation of simulated HAZ microstructures with hot ductility properties of the alloy revealed that the temperature at which the alloy exhibited zero ductility during heating was within the temperature range at which grain boundary liquation was observed. The on-cooling ductility of the alloy was significantly damaged by the on-heating liquation reaction, as reflected by the considerably low ductility recovery temperature (DRT). Important characteristics of the intergranular liquid that could influence HAZ microfissuring of the alloy in overaged condition are also discussed.

Microstructural Analysis of Laser-Beam-Welded Directionally Solidified INCONEL 738

Abstract: The laser welding of a directionally solidified INCONEL 738 superalloy (DS IN738) was investigated. Microstructural analysis of the fusion zone (FZ) and the heat-affected zone (HAZ) revealed that cracking occurred mainly in HAZ with only some cracks being extended into the FZ. However, the frequently observed centerline cracking in FZ of DS and single crystal (SX) alloys did not occur, which was attributed to the presence of negligible volume fraction of γ-γ′ eutectic in FZ. Constitutional liquation of secondary solidification constituents (MC carbides, M3B2 borides, M2SC sulphocarbides, and γ-γ′ eutectic) and γ′ precipitate particles was found to be the major cause of grain boundary liquation and the resultant intergranular microfissuring in the HAZ. The extent of HAZ microfissuring was, however, observed to be smaller in samples welded along the transverse direction (perpendicular to solidification direction) than when welding was done along the longitudinal direction (solidification direction). Nonetheless, more severe HAZ cracking occurred in samples of similarly welded conventionally cast (CC) alloy, and the present results indicate that the severity of HAZ liquation cracking in IN738 superalloy can be reduced by using a DS version of the alloy.

Dissimilar Friction Stir Welded Joints between 2024-T3 Aluminum Alloy and AZ31 Magnesium Alloy

Abstract: Dissimilar alloys such as 2024-T3 Al alloy and AZ31 Mg alloy of plates in 3 mm thickness has been friction stir butt welded. The welding was carried out at a constant rotation speed of 2500 min -1 and welding speeds of 200, 300, 400 and 550 mm/min. Effects of welding speeds on microstructures and hardness distributions of the joints were investigated. Distribution of phases in the stir zone (SZ) was analyzed by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS). Increasing welding speed brought about a redistribution of phases in SZ where the regions occupied by 2024 Al alloy concentrated in the lower portion of SZ while AZ31 Mg alloy concentrated in the upper region beneath the tool shoulder. The laminated structure was formed in the SZ near the boundary between SZ and TMAZ on the advancing side of 2024 Al alloy regardless of the welding speed. The hardness value fluctuates in the SZ due to formation of intermetallic compounds that formed by constitutional liquation during welding.

Effect of preweld microstructure on HAZ liquation cracking of Rene 80 superalloy

Abstract: The objective of this work was to study the microstructure of as cast, solution treated and overaged Rene 80 superalloy before and after welding treatment. Studies focused on identifying heat affected zone (HAZ) liquation cracking mechanism and the effect of preweld microstructure on it. The formation of HAZ liquation cracking or microfissuring is found to be strongly dependent on constitutional liquation of grain boundary precipitates. These liquated precipitates in the as cast state contain MC carbides and particularly γ/γ' eutectic islands. While in the overaged condition they consist of the MC carbides and borides. Also HAZ grain boundary liquation and subsequent resolidification occur in overaged Rene 80 during welding. MC carbide liquation can be observed at the weldment of solution treated Rene 80 but the intensity of this liquation is not enough for liquid film formation and then cracking. X-ray mapping of MC carbide forming elements, give further evidence on the liquid film formation at h...

Liquation Cracking in Heat Affected Zone in Ni Superalloy Welds

Abstract: Precipitation hardened nickel-based superalloys are widely used in aero and industrial gas turbine engines due to their excellent high temperature strength and remarkable hot corrosion resistance. A drawback of many of these alloys is that they are very difficult to weld due to their high susceptibility to heat affected zone (HAZ) cracking, both during welding and post weld heat treatments (PWHT). Weld cracking in many of these alloys has been attributed mostly to constitutional liquatioin of grain boundary NbC precipitates. however, HAZ cracking has been observed in carbon-free superalloys as well, Therefore, research was initiated to examine grain boundary liquation and cracking in HAZs in a variety of Ni-based superalloys. It was found that intergranular cracking of grain boundaries involved liquation of several other phases, in addition to NbC, that were present in pre-weld microstructure of the alloy. These even included the primary strengthening phase,γ’, in a very widely used superalloy, Inconel 738. In addition, segregation of melting point depressant element B was also observed at gain boundaries in other superalloys, which also caused grain boundaries in HAZ to liquate and resulting in their cracking. An overview of microstructural aspects of different liquation phenomena involved and characteristics of the liquid film contributing to the HAZ microfissuring of nickel superalloys will be discussed in this presentation

Intergranular liquation cracking in heat affected zone of a welded nickel based superalloy in as cast condition

Abstract: The microstructures of the as cast and the heat affected zone (HAZ) of tungsten inert gas welded IN738 superalloy were studied. A different secondary solidification microconstituent was observed in front of some of γ–γ′ eutectic in interdendritic regions of the as cast alloy, which is likely formed by an invariant eutectic type reaction during the terminal stage of the ingot solidification. On welding, the alloy in as cast condition, suffered extensive grain boundary liquation cracking in the HAZ regions while the fusion zone was free of exclusive centerline cracking. Subsolidus liquation reactions of terminal solidification microconstituent, MC type carbides and γ′ precipitate particles present in the preweld alloy in considerable volume fraction, were observed to be major causes of HAZ intergranular liquation and the attendant cracking. Good wetting behaviour of the grain boundary liquid film possibly aided by surface active boron atoms released by the liquation of the terminal solidification re...

Aluminium-silicon-copper-magnesium series deforming alloy and its preparing method

Abstract: The invention discloses an Al-Si-Cu-Mg series distortion aluminum alloy and the manufacturing method The alloy is made up from 90-120wt% Si, 30-40wt% Cu, 03-06wt% Mg, <030% Fe, <020% Zn, and other impurity <=015wt%, and the rest is Al The method includes the following steps: smelting and refining the raw materials in reflecting smelter, after processing the allow liquation by Al-Sr intermediate alloy, gaining cast rod through hemicontinuous casting, extruding the cast rod and after forging and T6 thermal treatment to gain the product The tensile strength of the alloy is over 397MPa, and broken tensile stretch is 6%, and rigidity is 136-141HB It is mainly used to make wheel for vehicle and motorcycle, piston, bearing, bidirectional sloping cam plate, etc

Improving weldability of aged 25Cr–35Ni heat resistant steel/alloy 800 dissimilar welds

Abstract: Dissimilar welding between the aged 25Cr–35Ni (wt-%) heat resistant steel and alloy 800 is not successful due to liquation cracking in the heat affected zone of the aged steel. Microstructures, mechanical properties and weldability of the dissimilar weld were characterised using SEM and Varestraint test. The effects of a preweld solution annealing, heat input, interpass temperature and type of filler metal were investigated. It was found that the most important step to improve weldability and to reduce cracking susceptibility was solution annealing. A suitable annealing treatment was then proposed. It was concluded that dissimilar welding of alloy 800 to the aged 25Cr–35Ni steel can be successfully carried out under the conditions of solution annealing, low heat input and low interpass temperature using Inconel 82 or 617 filler metals.

Liquation Cracking in Aluminum Welds

Abstract: Liquation cracking in the partially melted zone (PMZ) of aluminum welds was studied. The PMZ is the region immediately outside the fusion zone where the material is heated above the eutectic temperature. Highly crack-susceptible alloys 2024 and 7075 were welded using gas-metal arc welding (GMAW) with filler metals 1100 and 4043, respectively. Circular-patch welds were made on 3.2 mm thick workpiece with full penetration, and single-pass welds were made on 9.5 mm thick workpiece with partial penetration. Liquation cracking was observed in all welds. Dualpass welds were also made on 9.5 mm thick workpiece, with overlapping between the penetration tips of the two partial-penetration passes made on the opposite sides of the workpiece. Liquation cracking was found in the first pass but not in the second pass. The results were explained using TfS (temperature vs. fraction solid) curves of the weld metal (WM) and the PMZ based on the following criterion proposed recently: liquation cracking can occur if WM fS > PMZ fS during PMZ solidification.

Microcracking susceptibility in dissimilar multipass welds of alloy 690 to type 316L stainless steel using La added filler metals

Abstract: The microcracking susceptibility in dissimilar multipass welds of alloy 690 to type 316L stainless steel was investigated by the Varestraint test and the multipass welding test using the four different stainless steels varying the amounts of impurity elements such as P and S, and using the nine different filler metals of alloy 690 varying the La content. In order to simulate the dissimilar weld metals, stainless steels were gas tungsten arc (GTA) welded using alloy 690 filler metals with varying the dilution ratio. Microcracks occurring in the reheated weld metals were classified into ductility dip, liquation and solidification cracks. The ductility dip cracking susceptibility decreased with increasing the La content in the weld metal, while the liquation and solidification cracking susceptibilities increased contrarily when the La content in the weld metal exceeded ∼0·03 mass-%. The relation among the microcracking susceptibility, the (P + S) and La contents in every weld pass of the multipass we...

Determination of the density of Pb-Sn melts and segregation phenomena on their crystallization

Abstract: The density of liquid lead-tin alloys (17.64, 25.34, 25.61, 26.07, and 33.88 at % Pb) has been determined using an γ-ray attenuation technique over the temperature range from the liquidus line to 750–1040 K. The experimental uncertainty of the density measurements is estimated to be within the range of ±0.20–0.25%. It has been shown that the temperature hysteresis of the melt density and thermal expansion, which was observed previously in several studies, disappears after stirring the melts. The distribution of the components through the height of the liquid and solid samples and its variation with time and during melting-crystallization has been investigated. The study shows that the melts do not segregate on long standing (about 4 hours) near the liquidus temperature. However, crystallization and melting of homogeneous Pb-Sn alloys is accompanied by liquation phenomenon, which is enhanced as the sample composition deviates from the eutectic one.

Method for producing large bimetal regulating nut

Abstract: The method includes following steps: casting and roughening inner cylindrical face from carbon steel to prepare basal body of nut in carbon steel; carrying out rust removing, degreasing, and drying processes for the basal body; putting the basal body into borax liquation, and heating to 850-900 deg.C; taking the basal body out from the borax liquation, removing redundant borax liquation from outer and inner surface of basal body of nut; then fixing nut in carbon steel on centrifuge rapidly, centrifugal casting brass alloy onto surface of inner cylindrical face of basal body of nut in carbon steel, materials and proportioning by weight of brass alloy are as following: Cu 60-65%, Zn 25-30%, Sn 1.5-5%, Mn 2.5-4%, Fe 1.5-3%, Ni 1-3%; taking bi metallic nut rough out from centrifuge, water cooling it to room temperature; process of removing stress, and shaping. Advantages are: low cost, reliable quality of product, and high production efficiency.

Numerical simulation of the liquating behavior of niobium carbide in heat-affected-zone during welding of a superalloy

Abstract: In order to predict the propensity of a superalloy to heat-affected-zone (HAZ) liquation cracking, Visual FORTRAN procedures were developed based on a heat transfer and mass diffusion model and the constitutional liquation of precipitate (NbC) at grain boundaries was simulated numerically. The results show that with the increase in the rate of welding thermal cycle, the solid dissolution of precipitate prior to liquation decreases and the thickness of liquid film produced by constitutional liquation increases. Higher heating rate inhibits the further melting of adjacent matrix and the solidification of liquid by liquid-to-γ mode in the subsequent thermal cycle. As a result, the residual liquid film still maintains a great thickness at the moment when temperature is down to the eutectic point, which will promote HAZ micro-fissuring. Finally, hot ductility tests on a low-expansion superalloy were performed to verify indirectly the conclusions drawn from the numerical simulation.

Glass crystal materials made from mineral and technogenic feedstock from Karelia

Abstract: Facing and decorative glass crystal materials were developed from mineral feedstock and technogenic wastes. The effect of the components present in the mineral feedstock in liquation and crystallization of the glasses was investigated. The materials obtained can be used in construction for facing walls.

Simulating the yield strength of cast alloys in the Al-Mg system

Abstract: A physical model has been developed for determining the yield strength of alloys in the Al-Mg system in the cast state. The model takes into account the heterogeneity of distribution of the alloying element caused by dendrite liquation, as well as distribution specifics of eutectic inclusions. It is demonstrated that peripheral layers of dendrite cells enriched in the alloying element do not make a significant contribution to the yield strength of a cast alloy.

Partial melting and re-solidification in partially melted zone during gas tungsten arc welding of AZ91 cast alloy

Abstract: During the welding of AZ91 cast alloy, the presence of eutectic β-Mg 17 Al 12 phase results in constitutional liquation in the original interdendritic regions and in the formation of a partially melted zone (PMZ). In this study, gas tungsten arc welding (GTAW) and partial melting (simulated using furnace, salt bath and Gleeble) experiments were conducted. The results show that practically there would not be a critical heating rate during the welding to prevent constitutional liquation. The gradual change of the re-solidification microstructure within PMZ from base metal side to weld metal side was characterized. A sharp transition from base metal to PMZ has been observed. It is found that the original partially divorced eutectic has become a more regular eutectic in most of the PMZ, although close to the fusion boundary the re-solidified eutectic is again a more divorced one. Proceeding the eutectic re-solidification, α-Mg re-solidified with a cellular growth resulting in a serrated interface. The morphological change affected by the peak temperature and cooling rate will be presented and explained.