Strength differential measurements in IN 718: Effects of superimposed pressure

Abstract

We realize that the 2.1 deg difference in orientation between the proposed and the Rong/Dunlop OR is small such that the latter might be derived by approximation due to a lack of detailed analysis at the atomic level. However, we cannot agree with the notion that the two are the same because the small angular difference can lead to large lattice strain at the interface with the M 2 C lathes having a finite width (ϳ20 nm, carbides "C" in Figure 2 [1] ), as observed in the present study.The comments on our article raised a good point in that the invariant line approach cannot explain the orientation of the longest axis of the M 2 C precipitates in ferrite. However, it fell short to elucidate the cause of the problem and to distinguish the two (lattice match and invariant line) methods in its argument. The invariant line method is based on the elastic continuum theory. Although the method relies on lattice mismatch data for its predictions, it disregards atomic (lattice point) match in its calculation. This can be readily understood by the fact that an invariant line derived in a lattice transformation is generally not required to coincide with the low-index lattice directions of both phases in question. As a result, it is often ineffective predicting particle orientations in coherent precipitation problems.For this reason, we did not resort to the invariant line approach for the prediction of the longest axis of the M 2 C carbides in our study. Instead, it was concluded that the small lattice mismatch and good atomic registration along the [100] ␣ /[2 0] C common direction controls the primary orientation of the carbide lathes. However, the orientation of the second longest axis of the lathes in the plane perpendicular to the longest axis cannot be determined accordingly. Our study indicated that the invariant line approach could give a satisfactory account of the orientation of the axis. The success could be attributed to the facts that the lattice mismatch in the two perpendicular directions on the (100) ␣ /(2 0) C common plane is very similar and the repeat distance along the two is close.It is understood that there are limitations to both the lattice match and invariant line approaches, [3] and neither could resolve all the orientation issues involved in the present problem alone. The lattice (atomic) match approach is expected to play a major role dominating precipitate orientations. The invariant line approach, on the other hand, becomes valid to the issue of the second axis of the M 2 C lathes when lattice match criterion fails to resolve. This latter orientation problem is nonexistent if the precipitates are viewed to be needle-shaped. Our experiments clearly showed, as well as others, [4,5,6] that the M 2 C carbides in these alloys were lath-shaped. Recent experiments on INCONEL* 718 (IN 718) indicate * INCONEL is a trademark of INCO Alloys International, Huntington, WV.that the yield and subsequent flow stress are significantly higher in compression than in tension [1] over a range of temperatures, exhib...

Integrating the Pressure-Sensitive Nonassociative Plasticity by Exponential-Based Methods

“…They also deduced that there should be a nonassociative flow rule with employing a plastic potential to have a good agreement with experiments. The same results were also concluded by Chait [10] for Titanium alloys, and by Gil et al [11], Iyer and Lissenden [12], and Lewandowski et al [13] for nickel base alloys such as Inconel 718.…”

“…(1) and (22), the plastic multiplier is acquired, as follows: = èP (12) áP = 0 ^ ¿P = èP Merging Eqs. (11) and (12), the subsequent connection will form éP = ys' (13) To regulate the evolution of the back stress, the succeeding Chaboche's nonlinear kinematic hardening is adopted…”

Brittle-to-ductile transitions and its relation to the deformability of cementite in fully pearlitic steels

“…Pearlitic steels have been widely used as structural materials. Possible parameters which control their mechanical properties are such as prior austenite grain size, block size, colony size, inter lamellar spacing and carbide thickness [1][2][3]. It is fairly in agreement that the inter-lamellar spacing controls the yield stress in the form:…”

Experimental and Numerical Simulation Investigation on Deep Drawing Process of Inconel 718 with and without Intermediate Annealing Thermal Treatments

“…Similar to the plastic flow and elastic behaviour, no appreciable difference was observed between the AR and PSTT states. Therefore, the use of a symmetric surface will not introduce too much error, as reviewed by Lewandowski et al [18].…”