Ni-based Powder Metallurgy Research Articles

Effect of micron-sized particles on the crack growth behavior of a Ni-based powder metallurgy superalloy

Generally, larger non-metallic inclusions have a negative influence on crack growth resistance due to the stress concentration effects that result from them appearing along the paths of crack growth. The in-situ tensile behavior for dog-bone-shape specimens of a Ni-based powder metallurgy FGH4096 superalloy including micro-sized particles has been investigated. The effect of the micron-sized particles on the initiation and propagation of cracks was studied through the in-situ tensile test. The mechanism of the in-situ tensile process was investigated using molecular dynamics methods. The results showed that the particle inclusions were basically micron-sized, including carbide particles, rare earth inclusions and composite inclusions in the FGH4096 superalloy. The carbide particles cracked themselves but did not become a source of a main crack. Many carbide particles near the main crack paths did not aggravate the propagation of the main crack under tensile behavior. Molecular dynamics simulation results showed that the crack was found to be preferable close of regions of atomic disorder, and a stacking fault area formed during deformation was found to effectively release the stress concentration and delay the occurrence of cracks. Crack initiation and propagation around a notch was also investigated in detail, by combining the experimental and computational results.

Temperature dependence of tensile deformation mechanisms in a powder metallurgy Ni–Co–Cr based superalloy with Ta addition

To further develop Ni-based powder metallurgy (PM) superalloys for aero-engines, it is critical to understand their deformation mechanisms at various service temperatures. For turbine disks, the tensile strength and absorbed impact energy are critical parameters. The varying stress during tensile deformation makes it essentially different from creep. In this study, a high-performance PM superalloy with various Ta contents was evaluated by tensile tests at different temperatures from room temperature to 815 °C. The relationship between the temperature and plastic deformation mechanisms was explored at multiple scales using scanning electron microscopy and transmission electron microscopy, and the temperature dependence of the deformation mechanism map was established. The results demonstrated that the main deformation mechanism gradually changed from antiphase boundary shearing to superlattice stacking fault shearing as the temperature increases. The extended stacking faults (ESFs) were the source of the microtwins, which extended within the individual grains and thickened with increasing temperature. In addition, a novel mechanism of ESF formation was observed, i.e., Shockley shearing separated by one layer of atoms. Furthermore, the effects of Ta on the tensile strength and plasticity in PM superalloys were discussed.

Effect of Micron-Sized Particles on the Crack Growth Behavior of a Ni-Based Powder Metallurgy Superalloy

Effect of Micron-Sized Particles on the Crack Growth Behavior of a Ni-Based Powder Metallurgy Superalloy

Quasi-static hot deformation behavior of a novel third-generation Ni-based powder metallurgy superalloy

Quasi-static hot deformation behavior of a novel third-generation Ni-based powder metallurgy superalloy A3 was investigated by hot compression tests and microscopy. The activation energy for hot working of the experimental alloy was about 867 kJ/mol. An instability domain existed in the processing map when the strain was 0.2, implying a plastic instability at the temperature range of 1080–1100°C and the strain rate range of 0.016–0.1 s−1. The power dissipation efficiency in processing maps indicated that optimum parameters for large deformation could be controlled at the temperature range of 1000–1030°C and the strain rate range of 0.001–0.01 s−1. It provided a reliable suggestion for hot processing during the manufacturing of such superalloy.

Hot deformation induced microstructure evolution of a novel as-extruded Ni-based P/M superalloy

ABSTRACT Hot extrusion (HEX) and isothermal forging (ITF) are two critical processing methods in manufacturing of Ni-based powder metallurgy (P/M) superalloys. Hot compressions with different parameters were performed on a novel Ni-based P/M superalloy in as-extruded condition to simulate ITF and the related microstructure evolution. The results revealed that the as-extruded alloy was fully recrystallised with no preferred orientation, while hot deformation at relatively high strain rate could induce the formation of <101> texture. Low-angle grain boundaries were formed due to the rearrangement of deformation-induced dislocations. The existence of high-angle grain boundaries led to dislocation pile-ups and resultant local stress concentration. The grains were remarkably refined after hot deformation due to dynamic recrystallisation and corresponding reduction of average grain size varied from 20 to 67%. The average particle size of γ′ phases enlarged after hot deformation through an Ostwald ripening process and varied from ∼142.5 to ∼235.0 nm in different conditions while their initial sizes were ∼137.2 nm. The effect of strain rate on the particle size of γ′ phases was much greater than the deformation temperature that exhibited a stronger influence on their area fraction.

The sharp drop in fatigue crack growth life at a critical elevated temperature for a PM Ni-based superalloy FGH97

The fatigue crack growth (FCG) experiments for Ni-based powder metallurgy (PM) FGH97 superalloy were performed from RT to 800 °C in air. It has been found that the FCG life decreases in an accelerated manner with an increase in temperature in the service temperature range, and a sharp drop in FCG life was noticed at the inflection point temperature (Tc) of about 800 °C. The fractographic and microstructural analyses were carried out to investigate the primary reason for the phenomenon of observed sharp drop. The obtained results indicate that the fracture transforms from transgranular to intergranular mode during the crack propagation under elevated temperature, and the transition point of fracture mode (ΔKT) also declines rapidly with an increase in temperature. At 800 °C, ΔKT appears even from the crack starts to propagate, which is closely related to the significant decline of FCG life. Combined with the calculated apparent activation energies of FCG, it can be inferred that the sharp drop in FCG life is primarily attributed to the dynamic embrittlement induced weakening of grain boundary, which dominates in the intergranular FCG stage at 800 °C. Further, the evolution of the fracture mechanism governing the FCG process under the conditions of different temperatures and stress intensity factor range (ΔK) has been discussed. With an increase in temperature in the service temperature range, the dominant mechanism of the intergranular fractures transforms from stress assisted grain boundary oxidation to dynamic embrittlement, which results in the sharp decline of FCG life at Tc.

Effect of Ti and Al on microstructure and partitioning behavior of alloying elements in Ni-based powder metallurgy superalloys

The microstructure and partitioning behaviors of alloying elements in the γ and γ′ phases in Ni-based powder metallurgy superalloys with different Ti and Al contents were investigated. The results showed that Ti and Al were mainly enriched in the γ′ phase, partially partitioned in the γ matrix, and slightly distributed in the carbides. Different Ti and Al contents in various alloys influenced the composition and amount of MC carbides but did not influence the MC carbides’ morphology. With increasing Ti and Al contents, γ + γ′ fan-type structures formed at the grain boundary, eventually resulting in a coarsened γ′ phase. In addition, the morphology of the secondary γ′ phase transformed from nearly spherical to cuboidal. The saturation degrees of Cr, Co, and Mo in the γ matrix were substantially improved with increasing Ti and Al contents.

Effect of Ta on the microstructure of high performance Ni-based powder metallurgy superalloys

The effect of Ta on the microstructures of nickel-based powder metallurgy superalloys with different Ta contents was investigated in experiments and thermodynamic calculations. The Ta element predominantly occupied the γ′ phase of the superalloys, with some incursion into the γ phase, and minimal presence in the MC carbide. By substituting part of the Ti-Nb alloy, the Ta element transforms (Ti-Nb)C into (Ti-Ta-Nb)C. The MC carbides and small amounts of M23C6 carbides were observed on the ribbon-like grain boundaries. The Ta addition little affected the primary γ′ phase, but greatly influenced the secondary γ′ phase. Ta promoted the splitting of the secondary γ′ phase, converting it to a more stable state. Increasing the Ta content increased the lattice constants of γ′ and γ and altered the degree of misfit between γ′ and γ, indicating a morphology change. The Ta content also influenced the formation of the tertiary γ′ phase.

Stability of γ′ multimodal microstructure in a Ni-based powder metallurgy superalloy

Multimodal size distribution of γ′ phase was obtained in a slow-cooling experiment following supersolvus solution treatment (1191°C). The morphology of the secondary γ′ particles exhibited splitting and protrusion instabilities. In the subsequent aging process (815°C), reverse coarsening was observed, i.e., the average precipitate size decreased with increasing aging time. Reverse coarsening slows the coarsening rate of the precipitates, increases the hardness of the alloy, and greatly improves the morphological stability of the γ′ phase.

Modeling of thermal deformation behavior near γ′ solvus in a Ni-based powder metallurgy superalloy

We used two different methods to model the thermal deformation behavior of a Ni-based powder metallurgy superalloy at large strains (>0.6) near the γ′ solvus. We concluded that the Artificial Neural Network model, rather than the strain-compensated Arrhenius model, describes thermal deformation behavior accurately under large strains during hot extrusion. Artificial neural network, a data-driven machine learning approach, is more suitable for predicting unknown deformation behavior in extreme conditions by data learning based on a known experimental dataset.

Hot deformation behaviors of a new hot isostatically pressed nickel based powder metallurgy superalloy

Abstract

Research on Drilling of Ni-Based Powder Metallurgy Superalloys

The application of Ni-based powder metallurgy superalloys materials was limited for its' difficult-to-machine, such as excessive tool wear, frequent tool change, short tool life, low productivity, and large amount of power consumption etc. So the studying of Ni-based powder metallurgy superalloys drilling process becomes extremely important. This paper mainly introduces the research status of drilling of Ni-based powder metallurgy superalloys materials and through synthesize considering cutting force and cost effective, we determined the optimal of cutting tool materials is carbide YG8 twist drill. The optimal parameters of drilling of Ni-based powder metallurgy superalloys: cutting speed of 15m/min, feed per tooth of 0.02mm/r. When the superalloys material is machined by standard twist drill, it is always appearing the failure modes of drilling.

EFFECT OF MICROELEMENT Hf ON THE MICRO- STRUCTURE OF POWDER METALLURGY SUPERALLOY FGH97

Microelement Hf added in Ni-based powder metallurgy (PM) superalloy can modify microstruc- ture and improve mechanical properties, such as stress-rupture life, creep resistance and crack growth resistance, and also benefit to eliminate notch sensitivity. So systematically studying the effect of microelement Hf on PM su- peralloy microctructure will help to comprehend its corresponding mechanism. The effects of microelement Hf on the morphologies, chemical compositions and content of g' phase and MC carbide in FGH97 PM Superalloy were investigated by means of SEM and physiochemical phase analysis. The results showed that Hf facilitated the pre- cipitations of g' phase and MC carbide, and changed chemical compositions of g' phase and MC carbide, the effect of Hf on the size and morphology of MC carbide was not obvious, while Hf greatly affected the size and morpholo-

High-Temperature Friction and Wear of Ag/h-BN-Containing Ni-based Composites Against Steel

In order to attain self-lubrication in a wide range of temperatures, Ni-based powder metallurgy (P/M) composites containing different amounts (8–20 wt%) of Ag were prepared, and their friction and wear characteristics were investigated against AISI 52100 steel at temperatures of 25, 400, and 600 °C. One composite containing 12 wt% Ag and 4 wt% h-BN was also prepared and tested under the same conditions to analyze the effect of addition of h-BN on the friction and wear behaviors. The composites mainly consisted of Ni-based solid solution, free tungsten, Ag, and BN as revealed by XRD and EDS analyses. The friction coefficients and wear rates were found to decrease with increasing temperature and amount of silver. The friction coefficients shown by the composites containing relatively higher amounts of silver were in the range from 0.25 to 0.16 with temperature increasing from RT to 600 °C. The wear rates of the Ag/h-BN-containing composites were approximately an order of magnitude lower than those of the Base Alloy (having no solid lubricant) at all the temperatures. The addition of 4 wt% h-BN resulted in slightly greater friction and wear in comparison to the composites containing only silver.