Weldability of Ni-Based Superalloys Waspaloy® and Haynes® 282® - A Study Performed with Varestraint Testing (original) (raw)
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Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications, 2018
High temperature Ni-based superalloys are largely used in components of aircraft engines which are subjected to high thermal (above 700°C) and structural loads. Investment casting has been traditionally implemented for the manufacturing of these components with different levels of complexity and size. However, investment casting of large and complex parts can entail some difficulties which lead to higher casting defect ratios and the need of repairing. Therefore, it is essential to develop easy to repair Ni-based superalloys castings, i.e., castings with an enhanced weldability or reduced weld cracking susceptibility. Improvement of weldability will also enable the combination of small size castings with forged and rolled components in welded structures reducing overall manufacturing costs and foundry capacity requirements. Cracking susceptibility of Ni-based superalloy castings is much greater in comparison with equivalent wrought components due to coarser and non-homogeneous microstructures, grain boundary segregations and particular chemistry which promote several cracking mechanisms during welding. A methodology based on Varestraint test (hot cracking test) is introduced to
Cracking susceptibility after post-weld heat treatment in Haynes 282 nickel based superalloy
Acta Metallurgica Sinica (English Letters), 2013
This paper presents a study of the standard post-weld heat treatment (PWHT) behaviour of autogenous laser welded γ' age-hardenable precipitation strengthened nickel based superalloy Haynes 282 (HY 282). The study involves a careful and detailed microstructural characterisation as well as an analysis of the weld cracking susceptibility during welding and Gleeble thermo-mechanical physical simulation. Various factors that could influence post-weld cracking in superalloys weld were experimentally examined. Our microstructural examination of the as-solution heat treated (SHTed) material and the thermo-mechanically refined grain material shows that intergranular heat affected zone (HAZ) cracking is observable in only the as-welded SHTed material. There was no indication of post-weld heat treatment cracking in all welded materials. Our conclusion, in this study, is that the chemistry of superalloy HY 282 which aids the preclusion/ formation of deleterious solidification microconstituents during welding as well as its relatively slow aging kinetics enhances its resistance to PWHT cracking.
Journal of Metallic Material Research, 2019
Hot cracking susceptibility of fillers 52 and 82 in 800H and 825 nickel-base superalloys was discussed using the Spot Varestraint test. The fillers of 52 and 82 were added into nickel-base superalloys via a gas tungsten arc welding (GTAW).Experimental results showed that the hot cracking sensitivity of the nickel-base superalloys with filler at high temperature was lower than that without filler. The hot cracking sensitivity had a slight effect when the filler 82 was added. The total length of crack was increased, the liquid-solid (L-S) two-phase range is higher so that the hot cracking susceptibility will be raised. The morphologies of cracks included the intergranular crack in the molten pool, molten pool of solidification cracking, heat-affected zone of intergranular cracks, and transgranular crack in the heat-affected zone.
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Welding journal, 1997
A finite element model has been developed to quantitatively evaluate the local thermomechanical conditions for weld metal solidification cracking in a laboratory weldability test (the Sigmajig test). The loading mechanism in the Sigmajig test was simulated by means of nonlinear spring elements. The effects of weld pool solidification on the thermal and mechanical behaviors of the specimen were considered. An efficient algorithm was developed to include the solidification effects in the material constitutive relations. Stress/temperature/location diagrams were constructed to reveal the local stress development behind the traveling weld pool where solidification cracking occurs. Based on the concept of the material resistance to cracking and the mechanical driving force for cracking, the calculated local stress in the solidification temperature range was used to explain the experimentally observed cracking initiation behaviors of a nickel-based superalloy single crystal under different welding and loading conditions.
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Advanced Materials Research, 2011
Fusion repair processes such as gas tungsten arc welding (GTAW) and laser welding have been introduced for repairing turbine parts made from Ni-based superalloy materials. The weld-repair of turbine parts is well established, however, the inherent susceptibility of ’ hardened superalloys to weld cracking remains an issue and has resulted in repair limitations for highly loaded areas of turbine parts. This study presents a view of the weldability of superalloys taking both, the impact of the weld process and the weld filler selection into consideration. This comprises the interpretation of specific process parameters into physical parameters controlling the weldability and cracking sensitivity such as thermal gradient in the weld pool and solidification speed. Alloy specific parameters of the weld filler material, such as melting point and solidification interval are studied and set in correlation with the solidification parameters during welding.
MATEC Web of Conferences
This research work focuses on the mechanical behaviour comparative assessment in conjunction with microstructural evolution characterization of Waspaloy® and Inconel® 718, following TIG and EB welding. Both of the forth-mentioned alloys are precipitation strengthened Ni-based superalloys, widely used in chemical, petrochemical and aerospace industries. More specifically, Waspaloy® is strengthened by the precipitation of the ordered fcc gamma prime intermetallic phase, γ΄ - Ni3(Al,Ti), while Inconel® 718 is mainly hardened by the ordered bct gamma double prime phase, γ΄΄ - Ni3Nb, in addition to γ΄. After both welding processes, samples of the above superalloys were subjected to appropriate post-weld heat treatment, according to SAE Aerospace Material Specifications. The mechanical response of the tested specimens is assessed via uniaxial tensile tests, combined with fractography. Furthermore, the microstructural characterization of TIG and EB welds is conducted by Scanning Electron M...
Weldability of the superalloys Haynes 188 and Hastelloy X by Nd:YAG
MATEC Web of Conferences, 2014
Requirements of aircraft parts welded becoming increasingly severe especially in terms of reproducibility of geometry and metallurgical grade of weld bead; laser welding is a viable method of assembly to meet these new demands by its automation to replace longer term the manual TIG welding process. The purpose of this study is to determine the weldability of Hastelloy X alloy by the butt welding process Nd: YAG laser. To identify influential parameters of the welding process (laser power, feed rate, focal diameter and flow of gas) while streamlining testing, an experimental design was established with the CORICO software that uses the graphic correlation method. The position of the focal point was fixed at -1/3 of the thickness of the sheet. The gas flow rate and the power of the beam seem to have a major role on the mechanical properties and geometry of the weld. The strength of the weld is comparable to that of base metal. However, there is a significant drop in the elongation at break of about 30 %. The first observations of the cross section of the weld by scanning electron microscopy coupled with EBSD analysis show generally a molten zone presenting dendritic large grain compared to the equiaxed grains of the base metals without a heat affected zone.
Materials Science and Technology, 2013
Microstructural, mechanical and weldability aspects in the similar and dissimilar welds of alloy 718 and alloy 500 nickel based superalloys have been investigated. Alloy 500 weld metal showed high tendency of titanium to the segregation. Coalescence of the microvoids led to propagation of hot solidification microfissures. The alloy 718 weld metal displayed the formation of Nb rich low melting eutectic type morphologies, which can reduce the weldability. The microstructure of dissimilar weld metal with dilution of 65 wt-% displayed semideveloped dendritic boundaries. The less segregation and decrease in the low melting eutectics caused less susceptibility of dissimilar weld to solidification cracking. The segregation elimination phenomenon has occurred in the heat affected zone of alloy 500. In the partially melted zone, remelted and resolidified regions have been observed. These locations provided sites for nucleation of liquation cracks. For the alloy 718 heat affected zone, dissolution of c0-Ni 3 Nb needle-like precipitations has taken place. It was the chief reason for sharp decline of the microhardness. The heat affected zone of alloy 500 revealed intense liquation cracking, in which the crack is initiated at the partially melted zone. The hot liquation cracking in the heat affected zone of Alloy 718 was observed as a result of c0-Ni 3 Nb dissolution.
Advanced Engineering Materials, 2006
In welds, in Ni based superalloys complex interactions between different physical processes are expected to occur. On heating to a temperature close to the solidus temperature, the eutectic phases will dissolve ( ). Regions heated below solidus, but above the c′ solvus temperature will lead to complete dissolution of c′ precipitates. On cooling, re-precipitation of c′ phase results in a wide range of sizes of c′ precipitation. Due to thermal stresses, the dislocation activity occurs in different regions of the weld. The focus of the current research was to evaluate the structural changes that occur in the weld of Ni-based single crystal alloys.
Contribution of Microstructural Constituents on Hot Cracking of MAR-M247 Nickel Based Superalloy
Archives of Metallurgy and Materials, 2018
The aim of this study is to investigate influence of selected parameters of gas tungsten arc welding on microstructure of MAR-M247 nickel based superalloy originating from turbine vane. MAR-M247 is a precipitation-strengthened superalloy which is widely used in aerospace engines. The main strengthening phase in this material is ordered L12 intermetallic γ' phase Ni3(Al, Ti). The surface of alloy was modified by electric arc in order to present microstructural changes in weld and heat affected zone. Investigation of the heat affected zone revealed that constitutional liquation of γ' particles and primary carbides is responsible for the formation of a liquid grain boundary layer which finally contributed to cracking. Scanning electron microscopy indicated high susceptibility to cracking of MAR-M247 alloy which is connected with high content of γ'-formers aluminum and titanium.