scholarly journals Weldability Evaluation of Alloy 718 Investment Castings with Different Si Contents and Thermal Stories and Hot Cracking Mechanism in Their Laser Beam Welds

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 402
Author(s):  
Pedro Álvarez ◽  
Alberto Cobos ◽  
Lexuri Vázquez ◽  
Noelia Ruiz ◽  
Pedro Pablo Rodríguez ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Laser Beam ◽  
Hot Cracking ◽  
Laves Phase ◽  
Hot Ductility ◽  
Alloy 718 ◽  
Weldability Tests ◽  
Cracking Mechanism ◽  
Haz Cracking ◽  
Si Content

In this work, weldability and hot cracking susceptibility of five alloy 718 investment castings in laser beam welding (LBW) were investigated. Influence of chemical composition, with varying Si contents from 0.05 to 0.17 wt %, solidification rate, and pre-weld heat treatment were studied by carrying out three different weldability tests, i.e., hot ductility, Varestraint, and bead-on-plate tests, after hot isostatic pressing (HIP) and solution annealing treatment. Onset of hot ductility drop was directly related to the presence of residual Laves phase, whereas the hot ductility recovery behaviour was connected to the Si content and γ grain size. LBW Varestraint tests gave rise to enhanced fusion zone (FZ) cracking with much more reduced heat-affected zone (HAZ) cracking that was mostly independent of Si content and residual Laves phase. Microstructural characterisation of bead-on-plate welding samples showed that HAZ cracking susceptibility was closely related to welding morphology. Multiple HAZ cracks were detected in nail or mushroom welding shapes, typical in keyhole mode LBW, irrespective of the chemical composition and thermal story of castings. In all LBW welds, Laves phase with a composition similar to the eutectic of the pseudo-binary equilibrium diagram of alloy 718 was formed in the FZ. The composition of this regenerated Laves phase matched with the continuous Laves phase film observed along HAZ cracks. This was strong evidence of backfilling mechanism, which is described as wetting and infiltration of terminal liquid along γ grain boundaries of parent material. The current results suggest that this cracking mechanism was activated in three-point intersections resulting from perpendicular crossing of columnar grain boundaries with fusion line and was enhanced by nail or mushroom weld shapes and narrow and columnar γ grain characteristics of castings. Neither Varestraint nor hot ductility weldability tests can reproduce this particular cracking mechanism.

scholarly journals Comparison of Hot Cracking Susceptibility of TIG and Laser Beam Welded Alloy 718 by Varestraint Testing

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 985 ◽  
Author(s):  
Pedro Alvarez ◽  
Lexuri Vázquez ◽  
Noelia Ruiz ◽  
Pedro Rodríguez ◽  
Ana Magaña ◽  
...  
Keyword(s):  
Grain Size ◽  
Laser Beam ◽  
Laser Beam Welding ◽  
Hot Cracking ◽  
Welding Parameters ◽  
Minor Effect ◽  
Alloy 718 ◽  
Material Source ◽  
Cross Sectional ◽  
Varestraint Test

Reduced hot cracking susceptibility is essential to ensure the flawless manufacturing of nickel superalloys typically employed in welded aircraft engine structures. The hot cracking of precipitation strengthened alloy 718 mainly depends on chemical composition and microstructure resulting from the thermal story. Alloy 718 is usually welded in a solution annealed state. However, even with this thermal treatment, cracks can be induced during standard industrial manufacturing conditions, leading to costly and time-consuming reworking. In this work, the cracking susceptibility of wrought and investment casting alloy 718 is studied by the Varestraint test. The test is performed while applying different welding conditions, i.e., continuous tungsten inert gas (TIG), low frequency pulsed TIG, continuous laser beam welding (LBW) and pulsed LBW. Welding parameters are selected for each welding technology in order to meet the welding quality criteria requested for targeted aeronautical applications, that is, full penetration, minimum cross-sectional welding width and reduced overhang and underfill. Results show that the hot cracking susceptibility of LBW samples determined by the Varestraint test is enhanced due to extended center line hot cracking, resulting in a fish-bone like cracking pattern. On the contrary, the minor effect of material source (wrought or casting), grain size and pulsation is observed. In fact, casting samples with a 30 times coarser grain size have shown better performance than wrought material.

scholarly journals Varestraint Testing of Selective Laser Additive Manufactured Alloy 718—Influence of Grain Orientation

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1113 ◽  
Author(s):  
Tahira Raza ◽  
Joel Andersson ◽  
Lars-Erik Svensson
Keyword(s):  
Weld Metal ◽  
Heat Affected Zone ◽  
Grain Orientation ◽  
Hot Cracking ◽  
Alloy 718 ◽  
High Angle ◽  
Electron Backscattered Diffraction ◽  
Varestraint Testing ◽  
Significant Difference ◽  
Haz Cracking

The effect of grain orientation on hot cracking susceptibility of selective laser additive manufactured Alloy 718 was investigated by Varestraint testing. Electron backscattered diffraction showed that cracks in heat affected zone (HAZ) of the welded samples occurred in high angle grain boundaries. The extent of HAZ cracking was smaller in samples tested parallel to the elongated grain orientation and larger in samples transverse to the elongated grain orientation. However, for solidification cracking in the weld metal, no significant difference with respect to grain orientation in the base metal was found.

A Novel Method of Estimating the Laves Phase in Electron Beam Welded Alloy 718

2008 ◽  
Vol 45 (6) ◽  
pp. 271-282
Author(s):  
K. Sivaprasad ◽  
S. Ganesh Sundara Raman ◽  
A. Sambasiva Rao
Keyword(s):  
Electron Beam ◽  
Laves Phase ◽  
Alloy 718 ◽  
Novel Method

Hot Cracking Susceptibility of Nickel Base Alloy 718

1997 ◽  
Vol 30 (3) ◽  
pp. 14
Author(s):  
V. Shankar ◽  
G. Srinivasan ◽  
B. G. Muralidharan ◽  
T. P. S. Gill ◽  
V. K. Sethi
Keyword(s):  
Base Alloy ◽  
Hot Cracking ◽  
Alloy 718 ◽  
Nickel Base Alloy ◽  
Nickel Base

Hot cracking in autogenous welding of 6061-T6 aluminum alloy by rectangular pulsed Nd:YAG laser beam

2020 ◽  
Vol 64 (6) ◽  
pp. 1077-1088
Author(s):  
Hossain Ebrahimzadeh ◽  
Hassan Farhangi ◽  
Seyed Ali Asghar Akbari Mousavi
Keyword(s):  
Aluminum Alloy ◽  
Laser Beam ◽  
Nd:Yag Laser ◽  
Hot Cracking ◽  
Pulsed Nd:Yag Laser

A Smoothed Particle Hydrodynamics Model for Laser Beam Melting of Ni-based Alloy 718

2019 ◽  
Vol 78 (7) ◽  
pp. 2377-2394 ◽  
Author(s):  
Johannes Weirather ◽  
Vladyslav Rozov ◽  
Mario Wille ◽  
Paul Schuler ◽  
Christian Seidel ◽  
...  
Keyword(s):  
Laser Beam ◽  
Smoothed Particle Hydrodynamics ◽  
Alloy 718 ◽  
Laser Beam Melting ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

scholarly journals The Cracking Mechanism of Ferritic-Austenitic Cast Steel

2016 ◽  
Vol 16 (4) ◽  
pp. 153-156 ◽  
Author(s):  
G. Stradomski
Keyword(s):  
Chemical Composition ◽  
Cast Steel ◽  
Hot Cracking ◽  
Hadfield Steel ◽  
Structural Factors ◽  
Low Carbon ◽  
Secondary Phases ◽  
High Tendency ◽  
Iron Manganese ◽  
Low Solubility

Abstract In the high-alloy, ferritic - austenitic (duplex) stainless steels high tendency to cracking, mainly hot-is induced by micro segregation processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier papers [1 - 4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and / or ledeburite segregated at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very “rich” chemical composition and related with it processes of precipitation of many secondary phases.

scholarly journals Laser Beam Welding of a Low Density Refractory High Entropy Alloy

Metals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1351 ◽  
Author(s):  
Evgeniya Panina ◽  
Nikita Yurchenko ◽  
Sergey Zherebtsov ◽  
Nikita Stepanov ◽  
Gennady Salishchev ◽  
...  
Keyword(s):  
Laser Beam ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Laser Beam Welding ◽  
Base Material ◽  
Laves Phase ◽  
High Entropy Alloy ◽  
High Entropy ◽  
Grains Refinement ◽  
Cast Condition

The effect of laser beam welding on the structure and properties of a Ti1.89NbCrV0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T ≥ 600 °C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particles. A columnar microstructure was formed in the welds; the thickness of the grains increased with the temperature of pre-heating before welding. The Laves phase particles were formed in the seams after welding at 600 °C or 800 °C, however, these particles were not observed after welding at room temperature or at 400 °C. Soaking at elevated temperatures did not change the microstructure of the base material considerably, however, “additional” small Laves particles formed at 600 °C or 800 °C. Tensile test of welded specimens performed at 750 °C resulted in the fracture of the base material because of the higher hardness of the welds. The latter can be associated with the bcc grains refinement in the seams.

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