HOT LINE: +86-510-80628100GH4169 alloy is a solid solution aging strengthened nickel based deformation high-temperature alloy with γ 'and γ' 'as the main strengthening phases. This alloy has multiple types of elements, high degree of alloying, and good comprehensive properties such as high strength and good plasticity. It can be used for a long time at temperatures below 650 ℃. GH4169G alloy is an improved deformation high-temperature alloy developed on the basis of GH4169 by adding appropriate amounts of trace elements such as P and B. It not only maintains the original mechanical properties of GH4169, but also increases the service temperature of creep and durability performance by 30 ℃, reaching 680 ℃.
GH4169G alloy was selected for the trial production of high-pressure front/rear baffle forgings for a certain engine. Since the trial production, this type of forging has been manufactured by different suppliers, and there are varying degrees of mechanical properties and grain size that do not meet the requirements of forging during factory inspection.
Experiment and Analysis Discussion
Analysis of Persistent Sample with Gap Cycle
The notch cycle durability of GH4169G alloy is very sensitive to notches, and the size of the notch has a significant impact on the test results. During the first inspection, the notch r of the notch cycle durability sample was smaller than the technical requirements. The smaller the notch r, the greater the stress concentration factor, and the more likely fatigue cracks are to occur at the notch, reducing the notch cycle durability of the forging.
High magnification microstructure analysis of the entire cross-section of forgings
The carbide, carbonitride, and δ phases in the entire cross-section of the forging meet the technical requirements, and there is no Laves phase. However, there is heterogeneity in the organization, with most grains being grade 8, a small number being grade 6, and a few being grade 4, with a large range of step differences. The grain boundaries and δ phases within large grains are relatively few, and δ phase precipitation is depleted.
Discussion and analysis
The finer the grain size and the more grain boundaries, the greater the hindrance to dislocation movement; And a certain amount of δ phase precipitates on the grain boundaries, hindering further dislocation movement and increasing material strength. Meanwhile, more grain boundaries can activate more slip surfaces, resulting in uniform deformation and reducing crack initiation. The grain boundary strengthening phase δ is Ni3Nb phase, which has the same atomic composition as the main strengthening phase γ ''. When the δ phase precipitates, Nb atoms are occupied, resulting in depletion of the micro area γ '' around the δ phase and the formation of a plastic deformation zone, which can reduce local stress concentration. Uniform grain size and precipitation of δ phase can reduce crack initiation and prevent further crack propagation.
In this batch of forgings, it can be seen from the full section microstructure that the grain size is not uniform, and the precipitation of large grain boundaries and the δ phase inside the grains is depleted. When external forces are applied, the strengthening effect of grain boundaries weakens, and the grain boundaries parallel to the direction of external stress first undergo relative sliding, leading to the initiation of cracks and their propagation along the large grain boundaries, ultimately resulting in the poor high-temperature durability of the forgings.
Conclusion
(1) The notch cycle durability performance of GH4169G alloy is very sensitive to notches, and the radius of the notch has a significant impact on the performance. The main reason for the unqualified notch cycle durability performance of this batch of forgings is that the radius of the notch in the sample is smaller than the technical requirements.
(2) The GH4169G rear baffle forgings in this batch have locally deformed mixed crystal structures, with large grain boundaries and depleted δ phase, which is the reason for the unqualified high-temperature durability performance.
