scholarly journals Effect of heat treatment and heat-to-heat variations in the fatigue-crack growth response of Alloy 718

1980 ◽  
Author(s):  
L James ◽  
W Mills
Keyword(s):  
Heat Treatment ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Response ◽  
Alloy 718

scholarly journals Effect of Heat-Treatment Upon the Fatigue-Crack Growth Behavior of Alloy 718 Weldments—Part I: Macroscopic Behavior

1985 ◽  
Vol 107 (1) ◽  
pp. 34-40 ◽  
Author(s):  
L. A. James ◽  
W. J. Mills
Keyword(s):  
Heat Treatment ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Crack Growth Behavior ◽  
Alloy 718 ◽  
Gas Tungsten Arc ◽  
Increasing Temperature ◽  
Crack Growth Rates

Gas-tungsten-arc weldments in Alloy 718 were studied in fatigue-crack growth tests conducted at five temperatures over the range 24–649°C. In general, crack growth rates increased with increasing temperature, and weldments given the “conventional” post-weld heat-treatment generally exhibited crack growth rates that were higher than for weldments given the “modified” (INEL) heat-treatment. Limited testing in the as-welded condition revealed crack growth rates significantly lower than observed for the heat-treated cases, and this was attributed to residual stresses. Three different heats of filler wire were utilized, and no heat-to-heat variations were noted.

scholarly journals Effect of Heat-Treatment Upon the Fatigue-Crack Growth Behavior of Alloy 718 Weldments—Part II: Microscopic Behavior

1985 ◽  
Vol 107 (1) ◽  
pp. 41-47 ◽  
Author(s):  
W. J. Mills ◽  
L. A. James
Keyword(s):  
Heat Treatment ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Alloy 718 ◽  
Fatigue Crack Growth Behavior ◽  
Heat Treated

The microstructural features that influenced the fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination revealed that operative fatigue mechanisms were dependent on microstructure, temperature and stress intensity factor. All specimens exhibited three basic fracture surface morphologies at temperatures up to 538°C: crystallographic faceting at low stress intensity range (ΔK) levels, striation formation at intermediate values, and dimples coupled with striations in the highest ΔK regime. At 649°C, extensive amounts of intergranular cracking were observed. Laves and δ particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused an overall acceleration in crack growth rates at intermediate and high ΔK levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material were attributed to compressive residual stresses introduced by the welding process.

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