Microstructure and mechanical properties of Inconel 718 electron beam welds
TL;DR: In this article, a bead on plate, full penetration electron beam welds were produced in 2 mm thickness sheets of Inconel 718 in the solution treated condition, and they were subjected to an aging treatment with and without post-weld solution treatment.
Abstract: Bead on plate, full penetration electron beam welds were produced in 2 mm thickness sheets of Inconel 718 in the solution treated condition. Welds were subjected to an aging treatment with and without post-weld solution treatment. Weld microstructures, high temperature tensile properties and stress rupture properties were evaluated. The as welded fusion zone showed a considerable amount of interdendritic niobium segregation and brittle intermetallic Laves phase. The tensile and stress rupture properties of the welds after post-weld aging treatment were found to be inferior in relation to the base metal. Post-weld solution treatment at 980°C was found to result in partial dissolution of Laves phase, some reduction in niobium segregation and the formation of δ phase needles around the Laves particles. The use of 980°C solution treatment was found to improve the weld properties to some extent, although not to the level of the base metal. The reasons for this behaviour are discussed, correlating micro...
Citations
More filters
TL;DR: In this paper, the laser deposition process is optimized through a set of designed experiments to reduce the porosity to less than 0.03 pct, and failure modes of the tensile specimens were analyzed with fractography.
Abstract: Laser net shape manufacturing (LNSM) is a laser cladding/deposition based technology, which can fabricate and repair near-net-shape high-performance components directly from metal powders. Characterizing mechanical properties of the laser net shape manufactured components is prerequisite to the applications of LNSM in aircraft engine industrial productions. Nickel-based superalloys such as INCONEL 718 are the most commonly used metal materials in aircraft engine high-performance components. In this study, the laser deposition process is optimized through a set of designed experiments to reduce the porosity to less than 0.03 pct. It is found that the use of plasma rotating electrode processed (PREP) powder and a high energy input level greater than 80 J/mm are necessary conditions to minimize the porosity. Material microstructure and tensile properties of laser-deposited INCONEL 718 are studied and compared under heat treatment conditions of as deposited, direct aged, solution treatment and aging (STA), and full homogenization followed by STA. Tensile test results showed that the direct age heat treatment produces the highest tensile strength equivalent to the wrought material, which is followed by the STA-treated and the homogenization-treated tensile strengths, while the ductility exhibits the reverse trend. Finally, failure modes of the tensile specimens were analyzed with fractography.
393 citations
17 May 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a comparative study of high-cycle fatigue tests (T=650°C, f=110 Hz, R=0.1, Kt=1) were carried out with wrought Inconel 718 and LAMed Inconels 718, and the results showed that the influences of the Laves phases on highcycle fatigue properties are based on the applied stress amplitudes.
Abstract: In this paper, a comparative study of high-cycle fatigue tests (T=650 °C, f=110 Hz, R=0.1, Kt=1) were carried out with wrought Inconel 718 and LAMed Inconel 718. The results show that the influences of the Laves phases on high-cycle fatigue properties are based on the applied stress amplitudes. At a low stress amplitude, most of the Laves phases held their original morphologies. The fatigue cracks stopped in front or detoured around them, which means that the unbroken Laves phases play an important role in hindering crack propagation. In this way, the high-cycle fatigue life of LAMed Inconel 718 was superior to that of wrought Inconel 718. However, at a high stress amplitude almost all of the Laves phases in the crack propagation region splintered into smaller fragments, parts of which separated from the austenite matrix. Microscopic holes or cracks were formed at the interface, which provided passages for the fatigue cracks to propagate. In this case, the Laves phases were harmful, leading to the degradation of fatigue performance in LAMed Inconel 718 compared with wrought Inconel 718.
166 citations
TL;DR: In this paper, the microstructure and tensile properties of the Inconel 718 alloy were studied in the as-printed and different heat treat conditions, and the SLM as-print microstructures exhi...
Abstract: The microstructure and tensile properties of selective laser melted (SLM) Inconel 718 alloy were studied in the as-printed and different heat treat conditions. The SLM as-print microstructures exhi...
129 citations
Cites background from "Microstructure and mechanical prope..."
...In the interdendritic regions, due to segregation of heavy elements Nb and Mo, precipitation of Nb-rich laves phase occurs, which are actually detrimental to tensile, fatigue, and creep properties of the alloy [17]....
[...]
TL;DR: In this paper, the effects of pre-and post-weld heat treatments on the butt joint quality of 3.18mm thick Inconel 718 alloy were studied using a 4 kW continuous wave Nd:YAG laser system and 0.89mm filler wire with the composition of parent metal.
Abstract: The effects of pre- and post-weld heat treatments on the butt joint quality of 3.18-mm thick Inconel 718 alloy were studied using a 4 kW continuous wave Nd:YAG laser system and 0.89-mm filler wire with the composition of the parent metal. Two pre-weld conditions, i.e., solution treated, or solution treated and aged, were investigated. The welds were then characterized in the as-welded condition and after two post-weld heat treatments: (i) aged, or (ii) solution treated and aged. The welding quality was evaluated in terms of joint geometries, defects, microstructure, hardness, and tensile properties. HAZ liquation cracking is frequently observed in the laser welded Inconel 718 alloy. Inconel 718 alloy can be welded in pre-weld solution treated, or solution treated and aged conditions using high power Nd:YAG laser. Post-weld aging treatment is enough to strengthen the welds and thus post-weld solution treatment is not necessary for strength recovery.
115 citations
TL;DR: In this article, modified cyclic solution heat treatment showed reduction of microfissures and improved tensile and fatigue properties of large-grained Inconel 718 (ASTM #4 and #10).
Abstract: CO2 laser welding characteristics of Inconel 718, heat treatment effects on microstructures, and tensile/fatigue properties were researched. CO2 laser welding was carried out on 5 mm thick plates having two different grain sizes, ASTM #4 and #10. For the fine-grain sized specimens (ASTM #10), the optimum laser welding conditions without defects were 6 kW with 2.5 m/min and 8 kW with 4.0 m/min. However, on the heat-affected zone (HAZ) of large-grained Inconel 718 (ASTM #4), the microfissures were shown at the same welding conditions. Before welding, plates were pre-heat treated at three different conditions: as-received, 955 °C solution treatment, and 955 °C solution treatment + aging (955STA). After welding, welds were subjected to four different post-weld heat treatment conditions: as-welded, 955 °C solution treatment + aging, modified cyclic solution treatment, and direct aging (DA) treatment. In this research, modified cyclic solution heat treatment showed reduction of microfissures and improved tensile and fatigue properties.
112 citations
References
More filters
01 Jan 1973
TL;DR: In this article, the precipitation microstructure varies rapidly with aging temperature and composition, and the influence of composition and aging temperature on the conditions that bring about this compact morphology has been investigated.
Abstract: The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.
428 citations
TL;DR: In this paper, the authors used an integrated analytical approach to generate a constitution diagram for INCONEL 718* in the temperature range associated with solidification, where the important features of the diagram are an austenite (γ)/Laves phase eutectic which occurs at ≈19.1 wt pct Nb and a Laves phase which contains ≈22.4 wt nb. The distribution coefficient for Nb was found to be ≈0.5.
Abstract: As part of a program studying weldability of Ni-base superalloys, results of an integrated analytical approach are used to generate a constitution diagram for INCONEL 718* in the temperature range associated with solidification. Differential thermal analysis of wrought material and optical and scanning electron microscopy, electron probe microanalysis, and analytical electron microscopy of gas tungsten arc welds are used in conjunction with solidification theory to generate data points for this diagram. The important features of the diagram are an austenite (γ)/Laves phase eutectic which occurs at ≈19.1 wt pct Nb between austenite containing ≈9.3 wt pct Nb and a Laves phase which contains ≈22.4 wt pct Nb. The distribution coefficient for Nb was found to be ≈0.5. The solidification sequence of INCONEL 718 was found to be (1) proeutectic γ, followed by (2) a γ/NbC eutectic at ≈1250°C, followed by (3) continued γ solidification, followed by (4) a γ/Laves phase eutectic at ≈1200°C. An estimate of the volume fraction eutectic is made using the Scheil solidification model, and the fraction of each phase in the eutectic is calculatedvia the lever rule. These are compared with experimentally determined values and found to be in good agreement.
335 citations
TL;DR: In this article, diffusion bonding and laser welding are considered for joining a wide range of materials of interest in the aerospace industry, as well as in many other industrial applications, and offer remarkable advantages over conventional fusion welding processes.
Abstract: Advanced materials generally require novel joining techniques. Developments in new materials research should be conducted hand in hand with work on weldability and joining capacity aspects. Sound joint quality for any new material has always been considered a milestone in a research and development scheme for a new material, particularly in terms of widespread applications. Better understanding of the microstructure-mechanical properties relationships of the bonded or welded joints will feed back to the materials development activities both in conventional and new materials areas. The two joining processes diffusion bonding and laser welding are considered in this literature review, since these processes are capable of joining a wide range of materials of interest in the aerospace industry, as well as in many other industrial applications, and offer remarkable advantages over conventional fusion welding processes. Of particular interest is the ability to join the more difficult aerospace alloys wi...
290 citations
TL;DR: In this article, the microstructural characteristics and segregational features in alloy 718 welds, with low heat inputs proving beneficial, were found to form in the interdendritic regions of the weld metals as a result of segregation.
Abstract: Weld heat input/cooling rate (affected by welding process, parameters, technique, tooling, etc.) was found to influence the microstructural characteristics and segregational features in alloy 718 welds, with low heat inputs proving beneficial. Laves phase formed in the interdendritic regions of the weld metals as a result of segregation. The morphology and composition of Laves phase depended strongly on heat input/cooling rate and influenced its response to subsequent homogenization post-weld heat treatment. The various factors affecting the formation and control of Laves phase in alloy 718 welds are highlighted.
245 citations
TL;DR: In this paper, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current, and the results show that the use of current pulsing refines the fusion zone microstructure, reduces the amount of laves phase and exerts a favourable influence on its morphology and improves the response of the fusion zones to post-weld heat treatment and weld tensile properties.
Abstract: The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.
168 citations