Showing papers on "Liquation published in 2009"
30 Aug 2009-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors investigated whether these two types of cracks act independently or are related with each other in terms of initiation and propagation as this can lead to enhancing the understanding of the hot cracking phenomena in these alloys.
Abstract: It is a known fact that 2024 aluminium alloy is susceptible to solidification cracking in the weld metal and liquation cracking in the base metal when welded with fusion processes. The main purpose of this study is investigating whether these two types of cracks act independently or are related with each other in terms of initiation and propagation as this can lead to enhancing the understanding of the hot cracking phenomena in these alloys. Laser welding whether continuous or pulsed has promising outlooks for welding heat treatable aluminium alloys. But the fast heating and cooling rates involved in pulsed laser welding give rise to unique successively repeating microstructural features which provides an interesting base for studying the cracks. Thus, the experimentation involved Nd:YAG pulsed laser welding of 2024 aluminium alloy. The observations indicate that liquation cracks in the partially melted zone of wrought base metal have strong association with solidification cracks in the weld metal and accordingly it is proposed that the liquation cracks act as a strong initiation sites for solidification cracks. It is also shown that healing of liquated grain boundaries through backfilling can have a significant role on resistance to liquation cracking in the partially melted zone and that in turn can affect tendency for solidification cracking in the weld metal.
104 citations
TL;DR: In this paper, a microstructural study of laser-beam-welded IN 738 superalloy was performed to better understand the causes of heat-affected zone (HAZ) cracking and to determine an improved approach of alleviating the weldability problem.
Abstract: Microstructural study of laser-beam-welded IN 738 superalloy was carefully performed to better understand the causes of heat-affected zone (HAZ) cracking and to determine an improved approach of alleviating the weldability problem. The HAZ cracks in the alloy were intergranular liquation cracks that resulted from the liquation reaction of both secondary solidification products (MC carbides and γ-γ′ eutectic) and solid-state reaction products (γ′ particles) present in the preweld material. In contrast to the expectation based on Chadwick’s equation, a reduction of grain boundary liquid film thickness did not produce a decrease in HAZ cracking owing to increased base alloy hardness that accompanied a preweld heat treatment designed to reduce the intergranular liquation. Moreover, a major factor limiting the effectiveness of an existing preweld heat treatment with low base alloy hardness in reducing HAZ cracking was found to be the formation of intergranular M5B3 boride particles during the heat treatment. These borides can widen the HAZ brittle temperature range (BTR) during weld cooling and increase the propensity for cracking. Based on the results, a new preweld heat treatment that induces a moderate hardness and precludes grain boundary boride formation was found and was shown to produce a significant reduction in HAZ cracking in the welded alloy compared to the most effective pre-existing preweld heat treatment.
54 citations
TL;DR: The role of carbide dissolution in the grain boundary liquation of the steel is described in this article, which leads to the production of near spheroidal solid grains in a liquid matrix, a microstructure suitable for the thixoforming process.
Abstract: The success of semi-solid metal processing mostly depends on the formation of suitable starting microstructure, which must consist of solid metal spheroids in a liquid matrix. Various methods of obtaining this structure have been established; they include recrystallisation and partial melting (RAP), strain-induced melt-activated (SIMA), or simple mechanical stirring, to name a few. These methods, as widely discussed, have mostly been applied with light alloys, mainly aluminium based. This article discusses solid–liquid structural break-up in M2 tool steel subjected to a direct re-melting procedure from the as-annealed condition. The role of carbide dissolution in the grain boundary liquation of the steel is described. This leads to the production of near spheroidal solid grains in a liquid matrix, a microstructure suitable for the thixoforming process. Microstructural examination revealed that carbide particles contained in bands at 1220 °C slowly disappeared with temperature. At 1300 °C, the solid grains seemed to be free from carbides. Most of the carbides had now re-precipitated at the grain boundaries. Thixoforming carried out at 1340 and 1360 °C revealed the thixotropic properties of the semi-solid metal slurries. The results indicate a widening of the range of potential routes to thixoformable microstructures.
41 citations
TL;DR: In this article, the effect of severe plastic deformation associated with friction stir processing (FSP) on grain boundary liquation and the attendant cracking of Inconel 738 superalloy was examined.
39 citations
TL;DR: In this article, the microstructural response of directionally solidified Rene 80 superalloy to gas-tungsten-arc (GTA) welding was investigated, and it was found that the grain boundaries embrittled the grain boundary in the heat-affected zone (HAZ) and caused microfissuring along the liquated grain boundaries.
Abstract: The microstructural response of directionally solidified Rene 80 (DS Rene 80) superalloy to gas-tungsten-arc (GTA) welding was investigated. Rapid heating during welding resulted in a significant grain-boundary liquation of solid-state reaction product γ′ precipitates, intergranular elemental segregation induced M5B3 borides, and secondary solidification constituents MC carbides and sulfocarbides, which were all present in the preweld heat-treated alloy. Liquation of these particles embrittled the grain boundaries in the heat-affected zone (HAZ) and caused microfissuring along the liquated grain boundaries. Nevertheless, contrary to the generally observed increase in HAZ cracking in superalloys with an increase in Ti and Al concentration, due to increase in the alloy’s hardness, significantly reduced cracking was observed in DS Rene 80 compared to the conventionally cast IN738 welded under the same conditions, despite its hardness being higher than that of IN738. This was related to the nature of base-metal grain- boundary intersections at the fusion-zone boundary in these materials.
38 citations
TL;DR: In this paper, the microstructure and cracking characteristics of MIG welded magnesium alloy (AZ91D) joint, and the effect of welding speed on cracking susceptibility have been investigated.
Abstract: The microstructure and cracking characteristics of MIG welded magnesium alloy (AZ91D) joint, and the effect of welding speed on cracking susceptibility have been investigated. The welded joint consists of primary α-Mg and divorced phases (eutectic α-Mg+eutectic β-Mg 17 Al 12 ), the latter mainly distributing along the α-Mg grain boundaries. Solidification cracking often occurred in the crater and was also observed at weld center line when welding speed was 300mm/min, which are associated with segregation of Mn, Al and Zn and high tensile stresses in the welds. Liquation cracking appeared in HAZ immediately adjacent to the fusion line when low welding speed was used (300mm/min). It is mainly related to the low welding speed resulting in increasing heat input and tensile stresses in the HAZ. It is favorable to decrease heat input for improving the susceptibility of hot cracking during MIG welding of magnesium alloys.
16 citations
TL;DR: In this paper, a combination of Gleeble thermo-mechanical physical simulation and analytical electron microscopy techniques was used to study non-equilibrium dissolution mode of an equilibrium phase, δ phase precipitates, during rapid heating in IN 718 superalloy.
Abstract: A combination of Gleeble thermo-mechanical physical simulation and analytical electron microscopy techniques was used to study non-equilibrium dissolution mode of an equilibrium phase, δ phase precipitates, during rapid heating in IN 718 superalloy. In contrast to the generally reported complete solid-state dissolution, the result revealed that the precipitates dissolved by liquation reaction, which is pertinent to weldability and hot formability behavior of Nb-bearing nickel-based superalloys.
13 citations
TL;DR: The microstructures of an Inconel 718 alloy subjected to rapid thermal and stress cycles have been investigated to explain those observed in the friction welded joint of the alloy as mentioned in this paper.
Abstract: The microstructures of an Inconel 718 alloy subjected to rapid thermal and stress cycles have been investigated to explain those observed in the friction welded joint of the alloy. The thermal and stress cycles were simulated with a Gleeble thermal and mechanical simulator. It turned out that the microstructural changes caused by the rapid heating cycle at peak temperatures of 1253–1553 K were almost in accordance with those reported in the previous papers about the solidification process of the alloy and phase diagram of Inconel 718 calculated by Thermo-Calc: (1) dissolution of film carbide and needle precipitates of (δ phase at grain boundaries at temperatures from 1253 to 1373 K, (2) dissolution of massive carbide (NbC) at 1373–1533 K, (3) liquation due to the eutectic reaction between γ phase and NbC at 1443–1533 K, and (4) melting of γ phase at 1553 K or higher. In the specimens heated to peak temperatures above 1473 K, γ/Laves eutectic were formed which were not detected in the as-received base meta...
12 citations
TL;DR: In this article, the results of a metallographic and orientation imaging microscopy study of weld cracking observed in the gas tungsten arc repair welds of a polycrystalline (IN738LC), a directionally solidified (Rene 80) and a proprietary single crystal (SX) alloy were reported.
Abstract: The repair of gas turbine components is of importance both commercially and scientifically to ensure cost effective repair schemes that will extend the lives of hot end components such as blades and stators. The present communication reports the results of a metallographic and orientation imaging microscopy study of weld cracking observed in the gas tungsten arc repair welds of a polycrystalline (IN738LC), a directionally solidified (Rene 80) and a proprietary single crystal (SX) alloy. The three alloys were welded with low, intermediate and high strength weld fillers, using a weld build-up approach rather than a conventional weld repair of a through thickness crack. This procedure would be applicable for example to worn area on the tips of turbine blades. Inhomogeneous initial microstructures and those from solidification processes led to extensive heat affected zone microfissuring in the IN738LC alloy, associated with MC carbide liquation, liquation of gamma prime (γ′), segregation of boron and ...
10 citations
TL;DR: In this article, a failed Al-Feld AA 2219-Aluminum Alloy (Al-Cu) storage tank was investigated, which revealed the presence of incipiently melted and solidified particles as a result of welding/repair welding along the grain boundaries and also within the grains nearer to weld fusion line.
9 citations
TL;DR: In this article, the authors investigated microstructural aspects of constitutional liquation in the aluminium alloy 2017A and determined its effect on corrosion behavior of this alloy, which was found that, due to rapid heating rate, coarse θ (Al 2 Cu) particles were melted by constitutional liquations and this way introduced strong susceptibility of 2017A alloy to intergranular corrosion.
TL;DR: In this article, microstructures forming in the friction welding of Inconel 718 alloy have been investigated in order to understand the phenomena occurring during the welding process and to determine the factor controlling the joint performance from a metallographic point of view.
Abstract: Microstructures forming in the friction welding of Inconel 718 alloy have been investigated in order to understand the phenomena occurring during the welding process and to determine the factor controlling the joint performance from a metallographic point of view. In the interfacial zone, liquation microstructures characterized by a eutectic structure consisting of γ and Laves phases, and Nb-rich microstructures along the grain boundary (Nb-rich GB microstructures) were observed, and their amounts increased with the friction time and pressure. The volume fractions of these liquation structures were greater in the flash than in the interfacial zone, suggesting that the liquid phase was preferentially expelled into the flash by friction pressure, compared with the solid phase. Since the liquid phase was rich in Nb, this preferential expulsion of the liquid phase caused the depletion of Nb, a major element for the precipitation hardening of the alloy. The depletion of Nb brought about a decrease in the hardn...
TL;DR: Tancret as discussed by the authors made a clarification on the nature of phase transformations dealt with in a recent article [F. Tancret, Computational Materials Science 4 (2007) 13-19].
Patent•
19 Aug 2009
TL;DR: In this article, a method for restraining the liquation of a large-sized steel ingot through multi-ladle composite casting, relates to a casting process for large sized steel ingots of metal molds of all grades below 600t.
Abstract: The invention discloses a method for restraining the liquation of a large-sized steel ingot through multi-ladle composite casting, relates to a casting process for large-sized steel ingots of metal molds of all grades below 600t, is applied to a casting process for carbon steel and alloy steel ingots under vacuum and non-vacuum conditions, and has restraint function on the liquation of all components of steel ingots made of various metal materials. The method comprises that: 1) a steel ingot mold is made of grey cast iron; 2) a riser head adopts a heat insulating riser head, and the taper thereof is between 8 and 16 percent; 3) the ratio of the height to the diameter of the steel ingot is 1:1-3:1; 4) the steel ingot is made of carbon steel or alloy steel; 5) different pouring ladles adopt different component ratios; and 6) the pouring process of different pouring ladles adopt different time intervals. The method designs the multi-ladle pouring technical proposal of the large-sized steel ingot, has good restraint function on the liquation of the large-sized steel ingots, and solves the prior problem of the liquation of the large-sized steel ingots in factories.
01 Jan 2009
TL;DR: In this article, the effect of rare earth metals (REM) on the microcracking susceptibility of multipass welds of alloy 690 was examined by using the La or Ce containing filler metals.
Abstract: The effect of the addition of rare earth metals (REM) to the weld metal on the microcracking susceptibility in the multipass welds of alloy 690 was examined by using the La or Ce containing filler metals. The amounts of the La and Ce in the filler metal were varied in several levels. The microcracking susceptibility of the reheated weld metal was evaluated by the spot and transverse-Varestraint tests using pre-welded specimens made by GTAW. The augmented strain levels were varied from 0.50–2.44%. Cracks that occurred in the reheated weld metal evaluated by the Varestraint test could be classified into three types; ductility-dip, liquation and solidification cracking. The ductility-dip cracking susceptibility could be significantly improved by adding 0.01–0.025mass%REM to the weld metal. Adversely, the excessive REM addition led to the liquation and/or solidification cracking in the weld metal. Microstructural analyses revealed that phosphide and sulphide of La or Ce were formed in the REM containing weld metals, and Ni-La or Ni-Ce intermetallic compound was additionally identified in the excessively REM containing weld metals. High temperature tensile test indicated that hot ductility of the weld metal was ameliorated by adding 0.01–0.03mass%REM, implying that the ductility-dip cracking susceptibility was decreased as a result of lowering the grain boundary segregation of impurity elements such as P and S due to the scavenging effect of REM. The liquation and solidification cracking in the excessively REM containing weld metals were considered to be due to the formation of liquefiable intermetallic compounds of Ni and REM. The multipass welding test confirmed that microcracks in the multipass welds of alloy 690 were completely prevented by using the filler metals containing approx. 0.03mass%REM.Copyright © 2009 by ASME
TL;DR: In this article, the authors investigated the geochemical characteristics of the Jinchuan mine and found that the type of ore body has features of both magmatic liquation and late reconstruction action, and the prospect of seeking new deep ore bodies within similar deposits is promising.
Abstract: The Jinchuan deposit is hosted by the olivine-rich ultramafic rock body, which is the third-largest magmatic sulfide Ni-Cu deposit in the world currently being exploited. Seeking new relaying resources in the deep and the border of the deposit becomes more and more important. The ore body, ore and geochemistry characteristics of the concealed Cu-rich ore body are researched. Through spatial analysis and comparison with the neighboring II1 main ore body, the mineralization rule of the concealed Cu-rich ore body is summed up. It is also implied that Cu-rich magma may exist between Ni-rich magma and ore pulp during liquation differentiation in deep-stage chambers, which derives from deep-mantle Hi-MgO basalt magma. It is concluded that the type of ore body has features of both magmatic liquation and late reconstruction action. It has experienced three stages: deep liquation and pulsatory injection of the Cu- and PPGE-rich magma, concentration of tectonic activation, and the later magma hydrothermal superimposition. In addition, the Pb and S isotopes indicate the magma of 16 concealed Cu-rich ore body originates predominantly from mantle; however, it is interfused by minute crust material. Finally, it is inferred that the genesis of the Cu-Ni sulfide deposit is complex and diverse, and the prospect of seeking new deep ore bodies within similar deposits is promising, especially Cu-rich ore bodies.
Patent•
19 Aug 2009
TL;DR: In this paper, a method for preparing an intermediate alloy for producing a key alloy wire, which comprises the following steps: placing high-purity gold of which the purity is not lower than 5N and micro-alloy element with the adding amount of not more than 1 percent into a vacuum induction melting furnace, introducing a protective gas into the furnace under the high vacuum condition (10Pa), inductively heating the materials by using vacuum intermediate frequency, and quickly chilling the molten alloy at a high temperature by adopting a leakage pouring process to form small granular (similar to ball shape
Abstract: The invention discloses a method for preparing an intermediate alloy for producing a key alloy wire, which comprises the following steps: placing high-purity gold of which the purity is not lower than 5N and micro-alloy element with the adding amount of not more than 1 percent into a vacuum induction melting furnace, introducing a protective gas into the furnace under the high vacuum condition (10Pa), inductively heating the materials by using vacuum intermediate frequency, and quickly chilling the molten alloy at a high temperature by adopting a leakage pouring process to form small granular (similar to ball shape) intermediate alloy. The intermediate alloy prepared by the method has even granular components, does not cause liquation, has no pollution, does not need to process, and is convenient to use. The method for preparing the intermediate alloy for producing the key alloy wire solves the problems of difficult control for burning trace added components and even distribution of alloy elements, and provides a high-quality blank for subsequent processing of superfine wires.
TL;DR: In this paper, the authors investigate the welding of an AISI 304 austenitic stainless steel using a nickel alloy filler metal: Inconel 625 and find that in the dendritic microstructure of the fusion zone there are inclusions and precipitates containing Ti and Nb.
Abstract: In elevated temperature environments, austenitic stainless steels and nickel alloys have a superior corrosion resistance owing to their high Cr content. These alloys are widely used in nuclear reactors components, in plants of energy generation that burn fossil fuel as well as in chemical and petrochemical industries. The aim of the present work is to investigate the welding of an AISI 304 austenitic stainless steel using a nickel alloy filler metal: Inconel 625. GTAW process, post weld heat treatment, mechanical and metallographic tests, and compositional analysis of the joint were carried out. A fundamental investigation was undertaken to characterize fusion boundary microstructure and to better understand the nature and character of boundaries that are associated with cracking in dissimilar welds. The results indicate that in the dendritic microstructure of the fusion zone there are inclusions and precipitates containing Ti and Nb. Near the fusion line liquation areas could be observed. These are probably caused by an eutectic with lower melting point than the AISI 304. Such a eutectic may be a site for initiation of stress corrosion cracking.
TL;DR: In this paper, the effect of Ce addition on microcracking susceptibility in the multipass weld metal of alloy 690 was investigated in order to improve the micro-cracks susceptibility in it.
Abstract: The effect of Ce addition on microcracking susceptibility in the multipass weld metal of alloy 690 was investigated in order to improve the microcracking susceptibility in it. The ductility-dip cracking susceptibility in the reheated weld metal could be greatly improved by adding 0.015-0.025mass%Ce to the weld metal. Conversely, the excessive Ce addition to the weld metal led to liquation and solidification cracking in the weld metal. Hot ductility of the weld metal at the cracking temperature was greatly improved by adding 0.01-0.03mass%Ce, implying that the ductility-dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of Ce. The excessive Ce addition to the weld metal resulted in the liquation and solidification cracking attributed to the formation of liquefiable Ni-Ce intermetallic compound. The multipass welding test confirmed that microcracks in the multipass welds were completely prevented by using the filler metal added 0.032mass%Ce.
TL;DR: In this article, the analytical solution of the problem of formation of dendritic liquation for different configurations of a Dendritic cell has been obtained; the use of this solution makes it possible to optimize melting processes from the viewpoint of the chemical inhomogeneity of ingots and billets.
Abstract: Based on the mathematical model, the analytical solution of the problem of formation of dendritic liquation for different configurations of a dendritic cell has been obtained; the use of this solution makes it possible to optimize melting processes from the viewpoint of the chemical inhomogeneity of ingots and billets.