Search

Precipitation hardening stainless steel (PHSS) possesses high strength, impact resistance, and corrosion resistance, making it extensively employed in aerospace, nuclear power equipment, and petrochemical industries. The precipitates and reversed austenite (RA) generated during heat treatment significantly influence the properties of PHSS. This study investigates the impact of aging temperature (480–620 °C) on PH 13-8Mo stainless steel. As the aging temperature increased from 480 °C to 620 °C, the yield strength (YS) and ultimate tensile strength (UTS) initially increased and then decreased, while the impact energy initially decreased and then increased. At an aging temperature of 510 °C, the strength and hardness reach their maximum values, indicating peak aging conditions. The microstructure after aging treatment is lath martensite, RA and NiAl. With increasing aging temperature, the size of NiAl precipitates increases, accompanied by a rise in RA content. The quantitative analysis assessed the contributions of various strengthening mechanisms (precipitation strengthening, solid solution strengthening, grain refinement strengthening, dislocation strengthening, etc.) to YS. Quantitative calculations revealed that the precipitation strengthening effect was most pronounced at an aging temperature of 510 °C. [ABSTRACT FROM AUTHOR]

This study reports the effects of post-annealing on the electrical reliability of a NiAl/SiO2 interconnect structure for potential use as post-Cu interconnect. Our materials characterization using transmission electron microscopy and secondary ion mass spectrometry discloses that annealing at elevated temperatures induced the diffusion of Al into SiO2: Al, for a 400 °C-annealed sample, diffused only to a few nanometers from the interface, forming a thin aluminum-rich oxide layer, while samples annealed at higher temperatures show an extensive Al diffusion and interfacial reactions. In a voltage ramp dielectric breakdown test, the 400 °C annealed sample shows the lowest breakdown voltage, possibly, due to the aluminum-rich oxide layer serving as a self-forming barrier while the samples annealed at higher temperatures display a drastic reliability degradation with the annealing temperature increasing. In addition, analyzing data acquired from time-dependent dielectric breakdown tests using the E-model helps us predict the lifetime of the 400 °C sample to be longer than 105 h at 1 MV/cm.

Intermetallic compounds with special physical and chemical properties are considered to be advanced materials. However, the brittleness at room temperature of intermetallic compounds leads to poor performance, which limits its widespread application in engineering. The objective of this study is to investigate the strengthening mechanism of the copper (Cu) on the microstructure and material performance of WC/NiAl/TiC composite coatings by the laser cladding process. The results reveale that Cu element has a significant effect on the microstructure evolution of the coatings by inhibiting coarse crystal formation. The refined microstructure of the layer had been realized. X-ray diffraction (XRD) analysis demonstrate a reduction in lattice spacing within the composite coating structure as the proper Cu is added. Furthermore, the addition of Cu contributed to an enhancement in microhardness (868.9 HV0.2) and wear resistance. With 3% copper been added, the wear loss of the coatings has been reduced by 81.13% and the average microhardness value has been increased by 1.4 times as well. Moreover, the chemical metallurgical bond is produced between the particles and bonding phase resulting in strengthened compactness within the layer acting as a physical barrier-like film that increases polarization resistance. [ABSTRACT FROM AUTHOR]

Due to their superior corrosion resistance at high temperatures, stainless steels have a wide range of applications in numerous industries (including chemistry, the petrochemical industry, the paper industry, and nuclear engineering), it is also utilized in the medical industry as an implant material. To enhance the outstanding qualities of stainless steel such as high temperature corrosion, surface coating methods are also used. Boronizing, nitriding, thermal spray coating, physical vapor deposition, chemical vapor deposition, and electro-spark deposition procedures are used to apply these coating processes to steel surfaces. The electro-spark deposition (ESD) coating technology is one of the most promising approaches in this area. Using high-frequency and high-current electric pulses, the ESD micro-welding procedure bonds electrode material to the surface of a metallic substrate. In this study, AISI 304 and AISI 316L stainless steels were coated with FeAl and NiAl intermetallics using the ESD method. First, suitable experimental parameters for ESD coating were established. Second, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the microstructures and phases that formed on the coated surfaces. Then, the surface hardness of the resulting layers was determined. Finally, the corrosion properties of intermetallic-coated stainless steels were determined using electrochemical methods and compared with each other. As a result, both the hardness values and corrosion resistances of both stainless steel sheets have increased with intermetallic coatings. [ABSTRACT FROM AUTHOR]

The effect of a minor amount of rare-earth element Nd addition (0.1 at%) on the microstructural properties, microhardness, and cyclic oxidation resistance of NiAl–Cr(Mo) alloy is investigated in detail. The microstructure of investigated alloys is composed of NiAl-based dendrites and a eutectic mixture whose components are NiAl and Cr(Mo) phases. The minor amount of Nd addition refines the microstructure and increases the microhardness considerably. The results of the cyclic oxidation tests reveal that the surface scales of both alloys are mainly consisted of α-Al2O3 and little amount of Cr2O3. A Cr(Mo)-rich layer is observed in the metal/oxide interface. With Nd addition, the oxidation resistance of Ni–33Al–31Cr–3Mo alloy is strongly improved. The Nd-added alloy exhibits lower oxidation mass gain and increased scale adherence. [ABSTRACT FROM AUTHOR]

Water vapor is ubiquitously present for energy conversion and combustion systems, yet its effect on the oxidation of crucial structure components of heat-resistant alloys remains elusive. Departure from the well-established phenomenon of exclusive alumina growth from the NiAl oxidation in dry O 2 , we demonstrate that the NiAl oxidation in H 2 O results in the precipitation of a significant number of metallic Ni clusters within the Al 2 O 3 scale by adsorbing Ni atoms from the alloy through a vacancy-assisted solute capture solute capture process of the enhanced oxide/alloy interface migration. The Ni clusters initially have a hcp structure at small sized, transitioning into an fcc structure when their size exceeds ∼12.5 nm. Using atomistic modeling, we show that the dissolution of a high concentration of H derived from H 2 O into the oxide scale is the key to stabilizing the hcp Ni structure. Subsequent coarsening of the hcp Ni clusters lowers the H concentration, leading to the hcp → fcc transformation. These results provide mechanistic insight into the effect of water vapor on the long-term stability of the structure alloys by influencing the oxidation-induced mass transport across the scale/alloy interface and microstructure evolution within the oxide scale. • NiAl oxidation in H 2 O results in the precipitation of metallic Ni clusters in the Al 2 O 3 scale. • The Ni clusters initially have the hcp structure at the small size and transform into the fcc structure at the size greater than ∼12.5 nm. • A high concentration of H derived from H 2 O into the oxide scale is the key to stabilizing the hcp Ni structure. • The coarsening of hcp Ni clusters lowers the H concentration and thus results in the hcp to fcc transformation. [ABSTRACT FROM AUTHOR]

In recent times, high temperature operated coatings are becoming popular as they offer protection against both elevated as well as harsh environment to improve wear performance. Herein, we investigated and demonstrated an in-situ high-temperature wear behaviour over nanodiamond reinforced nickel-aluminium composite coatings up to 873K. The composite coating offered a substantial reduction in wear rate and COF up to 873K. At 873K, wear rate reduced by 97.3%, and COF dropped by 95.24% over ND reinforced NiAl composite coating comparing it with NiAl coating. Further, the findings were attributed with the help of lubricating effect of ND, formation of protective carbide and oxide etc. layers. This impressive research can pave the way for effective protection of the components up to elevated temperatures (873K). • Study of wear properties from RT to 873K. • NA1D composite coating showed 95.2% reduction in COF. • Addition of 1 wt% NDs reduced the wear rate by 97.3%. • Enhanced wear properties attributed to formation tribofilm. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation of the NiAl alloy in the CO 2 and O 2 atmospheres is comparatively studied by a combination of electron microscopy characterization and first-principles calculations. It is shown that CO 2 accelerates the oxidation of NiAl alloy by the formation of a highly porous γ-Al 2 O 3 scale that is non-protective and follows the linear growth law. By contrast, the NiAl oxidation in O 2 results in a double-layered oxide scale consisting of an outer columnar γ-Al 2 O 3 layer and an inner equiaxed α-Al 2 O 3 layer, which is protective and follows parabolic growth law. Our first-principles calculations show that this accelerated NiAl oxidation in the CO 2 can be attributed to more ready decomposition of adsorbed CO 2 than adsorbed O 2 into atomic oxygen on defective γ-Al 2 O 3 surfaces, which leads to the inward γ-Al 2 O 3 growth by the infiltration of gaseous CO 2 through the cracked oxide scale toward the exposed NiAl alloy. These results provide new insights into the atomic origin of CO 2 -promoted alloy oxidation. • CO 2 accelerates the oxidation of NiAl alloy compared with O 2. • The oxidation of NiAl alloy in the CO 2 results in a highly porous γ-Al 2 O 3 scale. • CO 2 is more readily to decompose than O 2 on the defective γ-Al 2 O 3 surface. • The rapid decomposition of CO 2 creates atomic O for the fast oxide growth. • The defective oxide allows the infiltration of gaseous CO 2 for inward γ-Al 2 O 3 growth. [ABSTRACT FROM AUTHOR]

Development of new ultrahigh strength steels with high strength and high toughness requires thorough comprehension of nanoscale precipitation mechanisms. In this investigation, a comprehensive array of techniques including atom probe tomography, transmission electron microscopy, scanning electron microscopy, electron backscatter diffraction, small angle x-ray Scattering and thermodynamic calculations were employed. These methods unveiled an intriguing co-precipitation mechanism involving NiAl and carbide nanoparticles in a 2.2 GPa grade strength steel. The results demonstrate that the precipitation mechanisms of NiAl and carbides at different aging temperatures have a significant impact on the strength and toughness of the steel. Sub-micron ε-carbide at the interface of martensite lath and uniformly distributed NiAl cluster in the matrix are independent nucleation during the low-temperature aging process. The high distribution density of NiAl cluster in the matrix results in an increase in the impact absorbed energy of the steel to 136 J, albeit with a slight decrease in strength. On the other hand, the NiAl with minimal lattice misfit and low interfacial energy preferentially nucleates uniformly in the matrix, inducing the nucleation of M 2 C and increasing the number density of M 2 C precipitates at the secondary hardening temperature. The homogeneous precipitation of spherical NiAl, along with needle-shaped M 2 C in the martensite, significantly enhances the strength of the steel, with a tensile strength reaching up to 2216 MPa and an impact absorbed energy of 21 J. • Ultra-high-strength steel with an excellent combination of strength (above 2.2 GPa) and ductility (approaching 12%) was achieved through a new dual-precipitates design concept with controlled dual precipitation of nanoscale NiAl and M 2 C phases. • Sub-micron ε-carbide at the interface of martensite lath and uniformly distributed NiAl cluster in the matrix are independent nucleation during the low-temperature aging process. The high distribution density of NiAl cluster in the matrix results in an increase in the impact absorbed energy of the steel to 136 J • The staged precipitation characteristics between the dual-precipitation co-configuration under different aging temperature were first revealed by 3D-APT, HR-TEM and SAXS characterization. [ABSTRACT FROM AUTHOR]