Comparative Analysis Over Tribology Characterization of TiAlN and TiAlSiN PVD Coating On Plasma Nitride Alloy 20

The nickel-iron-chromium (alloy 20) is enriching by hybrid surface treatment through plasma nitride (PN) and physical vapor deposition (PVD) process. The plasma nitriding process takes 12 hours at 500°C. Potentiodynamic testing is used to characterize the corrosion performance of the treated material, followed by morphological analysis of the exposed surface; XRD, EDX, SEM, hardness, and tensile testing are used to investigate appropriate coating properties. Plasma nitride and hybrid PVD nickel-iron-chromium alloys exhibit perlite (γ + α ’) phases and martensite (γ + α) phases, respectively. The martensite microstructure ensures superior tensile strength and hardness. The pin-on-disc tribometer test proposes to analyze friction and hard-faced behavior in the dry sliding position. The inclusion of Si improves the adherent oxide film, resulting in a low wear rate in TiAlSiN alloy 20. Due to the presence of the passive film, TiAlSiN alloy 20 exposes the most passive region to attain better corrosion resistance.

Analysis of variant-pairing tendencies in lenticular martensite microstructures based on rank-1 connection

Herein, variant-pairing tendencies of lenticular martensite in an Fe–30Ni–0.3C (wt%) alloy are analyzed based on rank-1 connection at martensite/martensite junction planes (JPs) to facilitate the understanding of martensite microstructure. The degree of incompatibility (θ) at the JPs successfully explained their observed frequency; in the actual microstructure, variant pairs with a small θ form preferentially. The experimentally obtained JPs were consistent with theoretical ones. To the best of our knowledge, this is the first study to confirm the validity of variant-pair crystallography in steel based on rank-1 connection, both theoretically and experimentally. Diamond, composite-spear, and composite-kink clusters are considered. The cumulative θ at the JPs can suppress diamond cluster formation because it exceeds the θ of a single variant pair, and the diamond cluster is not observed experimentally. However, θ at the JPs cancel out in composite-spear (CS) and composite-kink (CK) clusters, but CK clusters are rarely observed experimentally, while a few CS clusters are observed. This demonstrates the analytical limitations of 2D approaches used to evaluate the frequency of variant pairs and clusters. These two variant clusters have a narrow window of 2D observation because the orientation relationships between JPs and intersection lines between two habit planes affect the areas of JPs.

Hydrogen diffusion and trapping in laser additively manufactured ultra-high strength AerMet100 steel

Hydrogen trapping and the permeation behavior of laser additively manufactured (LAM) AerMet100 steel with an as-deposited specimen (AD) and after three types of heat-treated specimens (BM, TBMM, and TM) was investigated. At least three types of different hydrogen traps were identified in each microstructure of LAM AerMet100 steel, including both reversible and irreversible H traps. For as-deposited microstructure, the main reversible H trap states are related to the precipitation of M3C carbides associated with a detrapping activation energy (Ed) of 17.3±0.2 kJ/mol. After heat treatment, the dominant reversible hydrogen trap states in the tempered martensite microstructure have a different Ed value of 19.3±0.5 kJ/mol, which is attributed to the precipitation of highly coherent M2C carbides. In comparison with the reported Ed value of ~21.4 kJ/mol for main reversible hydrogen traps in wrought AerMet100 steel, the less Ed value in LAM AerMet100 steel is closely related to the composition change of M2C carbides. In all of the H pre-charged samples, the diffusible and total H concentration of the TM specimen and the TBMM specimen are about 3-4 times higher than that of the AD specimen and the BM specimen. The TM specimen with tempered martensite microstructure has the highest diffusible and total H concentration due to its high density of dominantly reversible H traps. The effective hydrogen diffusion coefficient (Deff) of LAM AerMet100 steel is on the order of 10-9 cm2/s, and decreases with increasing density of dominantly reversible H traps brought about by heat treatment. Furthermore, compared with wrought AerMet100 steel of a similar yield strength (~1750 MPa), the LAM AerMet100 steel has a comparable Deff of about 2.8×10-9 cm2/s.

Effect of Heat Treatment Conditions on Corrosion Resistance of 0.28C–1.4Mn–0.3Si–0.26Cr Steel with Nb, Ti, and V Microadditions

The article presents the results of the research on the influence of heat treatment conditions on corrosion resistance of newly developed HSLA-type (High Strength Low Alloy) steel in selected corrosive environments. Laboratory tests were carried out with using a salt spray chamber, enabling the continuous spraying of brine mist (5% NaCl) during 96 h under high humidity conditions. Additionally, as part of corrosion experiments, tests were carried out using the gravimetric method, in which the intensity of corrosive processes was measured by the linear corrosion rate. The research conducted revealed that the best corrosion resistance was noted for steel with a high-temperature tempered martensite microstructure. Investigated 0.28C–1.4Mn–0.3Si–0.26Cr steel with Nb, Ti, and V microadditions can be used in offshore drilling constructions and production platforms exposed to salts present in sea water, chlorides, sulfates, carbonates, and bromides, among others.

Wear Resistance of Medium Carbon Steel with Different Microstructures

In this research, the tribological properties of different microstructures of medium carbon steel produced by either an austempered process or quenched-tempered process are investigated. The as-received samples with annealed microstructure (spherodized) are austempered to obtain a bainite microstructure or quenched-tempered to obtain a tempered martensite microstructure. The tribological performance of these microstructures was studied using a ball-on-disk UMT3 tribometer. The results indicated that both bainite microstructures and tempered-martensite microstructures produced better wear resistance than pearlite microstructures. At the same hardness level, the austempered disk specimens have less cracking due to higher fracture toughness compared to quenched and tempered steel. For the disks, tempered martensite microstructures produced more plastic deformation compared with bainite microstructures. Mild abrasive wear was observed on the harder disks, however, smearing wear was observed on the softer disks. Adhered debris particles were observed on the balls.

Properties of Passive Films Formed on Ferrite-Martensite and Ferrite-Pearlite Steel Microstructures

The effect of ferrite-pearlite and ferrite-martensite phase combinations on the passive layer properties of low carbon steel is investigated in a 0.1 M NaOH solution. Heat treatments were designed to obtain ferrite-pearlite and ferrite-martensite microstructures with similar ferrite volume fractions. Potentiostatic polarisation and electrochemical impedance spectroscopy (EIS) results demonstrated the lower barrier properties of passive films on ferrite-martensite microstructure compared to the ones formed on ferrite-pearlite microstructure. This was attributed to the higher donor density of the passive layer on ferrite-martensite samples, measured with Mott–Schottky analysis. This behaviour was explained by the complex microstructure morphology of the martensite phase that led to the formation of a more defective passive film.

Evaluation of Hydrogen-Assisted Cracking Susceptibility in Grade T24 Steel

The delayed hydrogen cracking test was performed to evaluate the hydrogen-assisted cracking (HAC) susceptibility of Grade T24 steel base metal and the simulated coarse-grained heat-affected zone (CGHAZ). The base metal did not fail after testing for up to 672 h. In contrast, the CGHAZ sample failed after about 2 h when charged from all four sides, and 4 h when charged only from the internal diameter (ID) surface. The higher HAC resistance of the base metal compared to the CGHAZ was due to the microstructure difference. The tempered bainitic-martensitic microstructure in the base metal was more resistant to HAC compared to the untempered martensite microstructure in the CGHAZ. Fractography analysis indicated the decarburized zone on the ID surface delayed the development of the critical hydrogen concentration in the CGHAZ, thus improving the HAC resistance. The HAC cracking initiated with an intergranular fracture, then transitioned to quasi-cleavage and microvoid coalescence. The fracture behavior was explained using Beachem’s model.