As-received Research Articles

Microstructure and high-temperature tribological properties of Ti–6Al–4V alloy treated by laser shock peening

The high-temperature wear resistance plays an important role for Ti–6Al–4V alloy components working in extreme environments, especially vital for avoiding unexpected failure. However, the reasonable method of surface modification should meet the requirement of improving in wear resistance and less decreasing in mechanical properties simultaneously, which brings a great challenge. In the present research, the laser shock peening (LSP) technique was applied to optimize the superficial layer of Ti–6Al–4V alloy by different processing. The microstructure, elastic modulus, nano-hardness and high-temperature tribology properties of the LSP processed Ti–6Al–4V were investigated to reveal the improving effect. The results demonstrate the LSP processing transforms the dual-size grain structure to relative homogeneous grain structure and forms the gradient nano-structure in superficial layer. With the increasing of LSP processing numbers, the density of geometrically necessary dislocation (GND) decreases obviously, but the density of statistically stored dislocation (SSD) rises significantly, which promotes the increase of total dislocation density compared with the as-received (AR) alloy. Due to the crystal evolution, the Ti–6Al–4V alloy with three-times LSP processing has the lowest wear rate which is less than half of the as-received state. The observations on worn surface and adjacent cross-sectional microstructure reveal the severe scratching and many inner microcracks in the AR sample but the slight scraping and few inner microcracks in the three-times LSP processed sample. Considering the elevated nano-hardness and elastic modulus, the improved tribological properties should be mainly attributed to the optimized microstructure and dislocation state by LSP processing. The present research provides a more reasonable method to improve the high-temperature wear properties of Ti–6Al–4V alloy.

Effects of multiaxial non-proportional cyclic pre-hardening on monotonic tensile and fatigue properties of 316L stainless steel

Effects of multiaxial non-proportional cyclic pre-hardening (CPH) treatment by performing tension–torsion cyclic test in a circular path on the monotonic tensile and fatigue properties of 316L austenitic stainless steel are studied. Results show that the circular path pre-hardening treatment significantly improves the yield strength but reduces the elongation of materials in comparison with the as-received (AR) material. Moreover, the fatigue resistance of 316L stainless steel after CPH treatment gets markedly degraded at the strain amplitude of 0.4 % with a 26 % decrease of fatigue life, however, the 62 % life increase is obtained at the lower strain amplitude of 0.2 %. Therefore, it is reasonable to believe that the CPH treatment can be regarded as an effective method to increase the fatigue resistance within a certain range of strain amplitude if the proper loading path and cycles of the multiaxial pre-hardening process are used. The different life variations at the high and low strain amplitudes are explained from the perspectives of macroscopic deformation energy and microscopic deformation modes based on EBSD and TEM characterizations.

Dynamic recrystallization of Ti-6Al-4V alloy promoted by laser shock peening

In this study, the influences of different numbers of passes of laser shock peening (LSP) on the surface microstructures of Ti-6Al-4V alloy were investigated. Especially, the microstructural evolution of the As-received (AR) sample and LSP treated samples was observed by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) observations. The results showed the grain size and the distribution of α, β phase have changed after the LSP process. After 1 LSP processing, the grain size is more uniform, the β phases were transformed from scattered and laminar characteristics to linear characteristics, while the α phases were parcelled by the β phases. After 2 LSP treatment, obvious grain refinement can be observed and the influence depth is deeper compared to the 1 LSP sample. After laser shock peeing processing, the material also has obvious dynamic recrystallization (DRX). Finally, the mechanism of microstructure evolution by LSP was revealed.

Exploring the creep and oxidation behaviors of four types of FeCrAl alloys through small punch test at 600 °C: Experiments and simulations

Four types of iron-chromium-aluminum (FeCrAl) alloys, composed of different elements, were used to investigate the creep performance and high-temperature oxidation resistance. The microstructures in the undeformed regions after the small punch creep test (SPCT) remained consistent with the as-received (AR) FeCrAl alloys, while the grain aspect ratio (GAR) decreased and grains elongated in the deformed regions. Amongst the four alloys, Q1 exhibited the worst oxidation resistance, whereas Q4 showed superior oxidation resistance due to the addition of Si. Precipitates were observed in the deformed regions after SPCT but not in undeformed regions, indicating that deformation had a positive effect on element segregation. Creep models including Norton power law, Monkman-Grant relationship, Larson-Miller Parameters, and Fracture-Time law were obtained. Calculation results from these creep models revealed that under low loads Q4 had lower minimum creep rate δm and longer creep fracture time tr compared to other alloys; however, Q3 demonstrated better performance in terms of δm and tr under high loads. This suggests a strong correlation between creep performance and loads. Additionally, finite element method (FEM) was employed to explore the effects of minor variation (±0.005 mm) in specimen thickness on SPT curves and SPCT curves. FEM results indicated that this slight variation alone did not account for discrepancies observed in load-deflection curves; deviations of ±6.1% for δm and ±6.3% for tr were found corresponding to specimens with 0.5 ± 0.005 mm thickness.

Electrochemical Behavior of an Alpha-Phase Titanium Alloy in Oxidizing Nitric Acid Environments: Influence of an Oxygen-Enriched Layer

The study focuses on establishing the influence of an oxygen-enriched layer (OEL) on the electrochemical properties of an alpha-phase titanium alloy, Ti-Al-Zr, in oxidizing nitric acid environments. Heat treatment was given to the material at 760°C for 700 h in air which resulted in the formation of an OEL on the surface. The electrochemical properties were studied and compared with as-received (AR) conditions by techniques like open-circuit potential (OCP), potentiodynamic polarization, chronoamperometry, and electrochemical impedance spectroscopy measurement. It was established that the presence of an OEL on the surface reduced the cathodic activity of oxidizing species on the material’s surface. The OCP value did not depend on the presence/absence of the OEL on the surface. The presence of the OEL on the surface promoted the formation of a protective passive film. The material with an OEL on the surface had a lower donor density as compared to the AR condition.

Microstructure dependent burst behavior of oxide dispersion–strengthened FeCrAl cladding

Oxide dispersion–strengthened (ODS) FeCrAl alloys are an advanced cladding material that combines the high-temperature steam oxidation resistance of conventional wrought FeCrAl with the irradiation resistance and high-temperature strength of nanostructured ferritic alloys. In the present study, the effect of microstructure on the performance of the ODS FeCrAl alloy system in light-water reactor–accident scenarios is evaluated using a combination of experimentation and modeling. ODS FeCrAl alloy with nominal composition Fe-12Cr-6Al-0.3Zr-0.3Y2O3 was produced into a thin-walled tube via high-precision tube rolling. A portion of the as-received (AR) tube was subjected to a full recrystallization heat treatment. Both variants were subjected to burst testing at Oak Ridge National Laboratory’s Severe Accident Test Station. The recrystallized tube exhibited burst temperature margins 200 °C higher than that of C26M, whereas the AR tube only achieved burst properties comparable to the wrought FeCrAl alloy. The burst experiments were simulated in the BISON finite element code through the development of new viscoplastic material databases for each heat treatment condition, informed by high temperature tensile tests of tube specimens and existing literature data on creep mechanisms. Finally, an ODS FeCrAl burst criterion was obtained using simulated burst experiments across the entire range of test conditions.

Accelerated corrosion of Ni-based alloys in molten chloride salts, due to Ni2Cr phase formation

To understand how the precipitation of long-range ordering (LRO) in alloys affects molten salt corrosion, two Ni-Cr model alloys—one in as-received (AR) condition, the other isothermally aged to contain MoPt2-type Ni2Cr-ordered precipitates, and both featuring the same Ni-33at%Cr composition—were tested for 500 hours in molten NaCl–MgCl2 salt at 550°C. Post-corrosion weight loss analysis and advanced microstructural characterization of the corroded alloys revealed (through comparison with the AR specimens) that the ordered phase significantly accelerated the corrosion process. This suggests that the loss of Cr atoms in the corroded Ni2Cr-ordered superlattice structure, which creates extra weakness for molten salt corrosion. In terms of high-temperature corrosion resistance, the results of this study emphasize the importance of phase stability when designing alloys for molten-salt applications.

Ultrastrong gradient nanostructured CSS-42L bearing steel and its enhanced wear resistance at elevated temperature

A gradient nanostructured surface layer was successfully fabricated on the CSS-42L(15Cr14Co12Mo5Ni) aerospace bearing steel by ultrasonic shot peening (USP) technology at room temperature. The original austenite in the as-received (AR) CSS-42L bearing steel was fully transferred into lath martensite by quenching and two cryogenic tempering cycles. The lath martensitic structure at the surface of the bearing steel was refined into nanoscale martensite phases with an average size of 33.9 nm after USP treatment. The microhardness of the gradient heterogeneous nanostructured CSS-42L bearing steel increased by approximately 39 % compared to that of the tempered bearing steel. The mechanisms of martensite refinement during the USP process were analyzed and discussed using advanced materials characterization methods. Dry sliding wear tests at elevated temperatures (500 °C) were conducted on the tempered and USPed CSS-42L bearing steel samples, respectively. The wear resistance of the USPed sample was significantly enhanced compared to that of its untreated coarse-grained counterpart. The wear rate coefficient of the USPed CSS-42L was reduced by 80.42 % compared to the AR sample. The superior wear resistance of the USPed CSS-42L bearing steel was attributed to the formation of an ultrastrong surface layer with a gradient heterogeneous nanostructure fabricated by USP technology.

Processing of automotive shredder residues: Economic evaluation of a process for energy and high-value metals recovery

Challenges in recycling heterogeneous waste remain untapped. Automotive shredder residue is one such heterogenous waste generated after processing End-of-Life Vehicles, making it difficult to process. There are two impediments to the recycling of ASR. One is the heterogeneity of the ASR (as received), and the other is not knowing what constituents to be extracted from the ASR. The ability of the thermochemical process to transform waste into beneficial products is well known. The objective of this work is based on a techno-economic evaluation of the recovery of energy and high-value metals from Automotive Shredder Residue. The equipment sizing and fabrication cost of each piece used in this process are calculated based on laboratory experiments. An integrated techno-economic study for processing heterogeneous waste ASR has not been studied in the literature previously. The economic evaluation was carried out assuming a plant life of 25 years. In addition, the plant's revenue was generated by the obtained products, and the payback period for energy and metal recovery was found to be 3 years respectively. The capital cost and operating cost for the ASR recycling plant with a combined approach of recovering energy and metals have been estimated from grass root stage. The outcome of this study confirms that ASR recycling has potential value for secondary resources and the process is economically viable. The resource recovery from ASR is an environmentally friendly technology where the maximum utilization rate is raised, along with energy saving and environmental protection by reduction of ASR waste in landfill.

Peculiarities of Fatigue Crack Growth in Steel 17H1S after Long-Term Operations on a Gas Pipeline.

This work presents the results of metallographic studies and the tensile, impact, and fatigue crack growth (FCG) resistance tests of 17H1S main gas pipeline steel in the as-received (AR) state and after a long-term operation (LTO). A significant number of non-metallic inclusions forming chains stretched along the direction of pipe rolling were found in the microstructure of the LTO steel. The lowest values of elongation at break and impact toughness of the steel were determined for the lower part of the pipe close to its inner surface. FCG tests at a low stress ratio (R = 0.1) did not reveal a significant change in its growth rate in degraded 17H1S steel compared to steel in the AR state. During tests at a stress ratio R = 0.5, the effect of degradation was more pronounced. The Paris' law region of the da/dN-∆K diagram for the LTO steel corresponding to the lower part of the pipe close to its inner surface was higher than those for the steel in the AR state and the LTO steel corresponding to the higher part of the pipe. Fractographically, a significant number of delaminations of non-metallic inclusions from the matrix were recognized. Their role in the embrittlement of steel, especially steel from the lower part of the pipe close to its inner surface, was noted.

Analysis of the effects of isothermal aging and Laser Shock Peening on the flow properties, fatigue crack growth, and fracture toughness of Inconel 718

Laser Shock Peening (LSP) is a surface treatment that improves the fatigue life and fatigue strength of components by inducing a shallow layer that is characterized by compressive residual stress and plastic deformation. This study investigates the use of LSP on Inconel 718 (IN718) on the fatigue crack growth (FCG) and fracture toughness (FT) of as-received (AR), solution-treated (SOL), and samples aged for 0.5, 4, and 100 h. Experimental results on aged samples established that the hardness of samples 0.5 and 4 h increased due to the precipitation of γ′ and γ″ phases while in the 100 h sample the hardness decreases due to the presence of coarser γ″ phase and intergranular δ-phase. These microstructural features impacted the plastic flow behavior of the different samples which was adequately described using a two-fitting approach to the Voce equation. While thermal aging accelerated the FCG of aged samples, the plastic flow and residual stress induced by the LSP significantly reduces the effect of thermal aging, by reducing the FCG rate and increasing the FT of the IN718 aged samples. Finally, results from EBSD analysis showed that the LSP-induced plastic strain depends on the microstructural transformations that occurred during the aging treatment.

Directional fretting wear behaviour of constrained groove pressed aluminium sheet

Wear behavior of the constrained groove pressed (CGP) aluminium (Al) sheet was examined along both the longitudinal as well as transverse direction using fretting wear tester. The results unequivocally showed a significant diminution (up to 1.2 times for one pass) in the coefficient of friction (COF) which leads to significant improvement in the wear resistance after each pass of CGP when compared to the as-received (AR) sample. Subsequently, wear rate in the CGP processed sample was found to be lower along the transverse direction (∼ 0.38 ± 0.08 ×102 µm3/N.mm) compared to that in the longitudinal direction (∼ 0.87 ± 0.12 ×102 µm3/N.mm) for one pass sample. Along longitudinal direction the major wear mechanism is discerned to be severe abrasion followed by crater formation in the samples with lower strain (i.e. 1 pass), however, it is delamination followed by dense tribolayer formation in the highly strained sample along transverse direction. Increasing fraction of oxygen content in energy dispersive spectroscopy result support the formation of dense tribolayer along transverse direction which attribute to formation of protective layer in the wear scar. The substantial decrement in the wear volume and hence wear rate after severe deformation is credited to the significant strain imposed in the sample, which leads to significant hardness up to ∼ 1.5 times for 3 pass CGP (44.5 VHN) due to the grain refinement from AR to 3 pass CGP i.e., ∼ 21.64 µm to ∼ 5.60 µm. Therefore, effect of grain refinement on the mechanical as well as wear properties with CGP on Al substrate has also been established.

Utilization of Rice Straw Wastes as Aggregate in Lightweight Concrete Block Production by Using Cold Press Technique

A massive rice straw waste was collected annually after the harvesting period. To reduce the air pollution/PM 2.5 during the burning season and to utilize those straw wastes, the development of rice straw based-lightweight cement block was studied. A Cold press method was selected for block manufacturing as it could gain terrific compressive strength with user-friendly operation. It was found that the saturated surface dry (SSD) condition of the straws achieved higher strength than that of the as-received (AR) condition. SSD of straw had softer and more flexibility to easily disperse in the cement matrix. Moreover, extra water in the wet SSD straws could also allow internal curing for more hydration reactions inside the specimens during their curing period. The optimal proportion for the production of rice straw based-lightweight cement block, achieving 6.43 MPa, is 0.30 of w/c ratio with 2% of straw addition in the SDD state. The outcomes could promote a value-added concept and achieve greener and cleaner production for the development of environmentally friendly alternative construction materials.

Deformation behavior and formability of friction stir processed DP600 steel

Abstract The effect of friction stir processing (FSP) on the formability of DP600 steel was experimentally investigated and the basic relationships between biaxial deformation behavior and FSP-induced evolutions in microstructural and mechanical properties were established. FSP formed a microstructure that consists of lath martensite with increased volume fraction compared to as-received (AR) microstructure that mainly consisted of well-distributed fine martensite particles in a ferrite matrix. Consequently, AR yield strength (301 MPa) and ultimate tensile strength (621 MPa) increased to about 811 and 1054 MPa, respectively. This strength enhancement achieved accompanied by adequate uniform elongation and elongation to failure values of 6.3 and 13.0%, respectively. Under biaxial loading conditions, good strain hardenability of the AR DP600 steel brought about a large membrane stretching regime leading to high punch force for biaxial flow. After FSP, both punch displacements within the membrane stretching regime decreased due to the increased volume fraction of lath martensite leading to higher cracking tendency. In result, cup depth and peak punch force of FSPed DP600 decreased from 8.7 mm and 33.2 kN to 7.1 mm and 28.1 kN, respectively. The obtained results simply indicate that FSP can be employed to enhance the strength of dual-phase steels with a reasonable level of formability.

Influence of induction hardening on the damage tolerance of EA4T railway axles

Induction hardening, a more efficient and effective surface hardening technique of railway axles, has received considerable attention for its potential of replacing deep rolling to be the surface strengthening technique of EA4T axles. In order to establish guidance for industrial utilization of induction hardened railway axles, damage tolerance assessment on induction hardened EA4T axles is a necessity. The purpose of this paper is to evaluate the influence of induction hardening on the damage tolerance of EA4T axles subjected to flying ballast impact damage. Impact damages were introduced artificially by means of shooting balls of 2 mm in diameter to induction hardened specimens and untreated ones. The damage modes of two kinds of specimens were analyzed and the resultant loading capacity debit was evaluated. Based on the characterization of damages and fracture surfaces, failure mechanisms were discussed. Due to the high strength of hardened layer, it is more significant to resist plastic deformation under a moderate impact. Under ballistic impact, microcracks, material loses and adiabatic shear bands (ASBs) present in damage of hardened specimen. Fatigue strength of smooth hardened specimen was improved by 61 % in comparison with that of untreated one. As a result of stable and considerable compressive residual stress of induction hardened (IH) specimen, fatigue strength of damaged hardened specimen is markedly larger than the as received (AR) ones with similar defect size.

Localised corrosion susceptibility of nitrogen-containing type 316LN stainless steel in cold work and thermally aged conditions

ABSTRACT In the present paper, an investigation was carried out to understand the microstructure or secondary phase changes formed during thermal ageing at nose temperature (where Cr diffusion was faster) and its influence on the pitting corrosion behaviour of type 316LN SS with marginally lower Cr in as-received (AR) and 10% cold work (CW). X-ray diffraction studies confirmed Cr23C6 and Cr2N in AR and CW conditions. On thermal ageing, AR material from 0 to 10 h and CW from 10 to 24 h, although with lower Cr, the degree of sensitisation (DOS) and pitting potential (E pit) were insignificant due to nitrogen where as above 10 h in AR condition and below 10 h in CW condition resulted reductions in pitting potential (E pit) in different chloride mediums. These results provide new insights on the interplay between pitting, microstructures, alloying elements.

Grain size dependant high-temperature hot corrosion (HTHC) degradation behavior in Alloy 617 during exposure in Na2SO4 + NaCl + V2O5 salt mixture

In the present investigation, the implication of grain size on the high-temperature hot corrosion (HTHC) response in Alloy 617 is studied. Towards this, specific thermal and thermo-mechanical processing schedules were employed to attain a wide range of grain sizes (7–70 µm), while maintaining other microstructural features like Σ3 n (n ≤ 3) boundary fraction, retained strain, and precipitate fraction nearly at constant. Subsequently, these specimens were exposed to Na 2 SO 4 + NaCl + V 2 O 5 (75 wt% + 20 wt% + 5 wt%) salt mixture at 1273 K for 24 h. Post-corrosion analyses reveal the formation of a highly porous and thick oxide scale on the as-received (AR) specimen (~32 µm), a relatively less porous and non-uniform oxide scale on the very coarse-grained specimen (~70 µm), and a homogeneous and dense Cr-rich scale on the very fine-grained microstructure (~7 µm). Such a protective scale on the very fine-grained specimen, developed due to the enhanced diffusivity of Cr, obstructs the entry of corrodents and thereby minimizes the percolation depth (~60 µm). The percolation depth is relatively higher (~130 µm) in the very coarse-grained specimen due to the development of a porous and non-uniform oxide scale. However, its percolation depth is still lower than the AR specimen (~ 305 µm), because of the reduced grain boundary area available for the diffusion of the corrosive species into the substrate. The AR specimen has exhibited the maximum percolation depth due to the simultaneous presence of fine and coarse grains, leading to the failure of both the aforementioned resistive mechanisms i.e., the accelerated formation of a protective Cr-rich scale and lesser availability of diffusion paths for the ingression of the corrosive species. • Very fine and very coarse-grained microstructures are resistant to HTHC damage. • AR specimen with inhomogeneous grain size distribution underwent maximum damage. • Grain refinement accelerates Cr-oxide formation that blocks entry of corrodants. • Grain coarsening decreases the channels for ingression of corrodants into the alloy. • Inhomogeneous grain size distribution in AR fails to activate resistive mechanisms.

Fatigue behaviour of laser shock peened AISI D2 tool steel

Laser shock peening (LSP) is an advanced surface enhancement technique capable of imparting beneficial compressive residual stresses, thereby improving metal parts’ fatigue resistance and crack propagation resistance. This study presents the fatigue behaviour of AISI D2 tool steel samples subjected to LSP with a power density of 15 GW/cm2 and a double laser scanning sequence. The effect of LSP on quasi-static tensile properties was also addressed. The fatigue crack propagation was suppressed in LSP-treated samples when tested at ΔK = 10 MPam. The fatigue strength of treated samples was 32.9% higher compared to untreated samples. The LSP-treated samples have shown a larger fatigue fracture surface area than the as-received (AR) sample. In addition, the tendency to form secondary cracks in the fatigue fracture paths decreased due to LSP treatment. LSP treatment can effectively improve the fatigue resistance and crack propagation behaviour of AISI D2 steel. These improvements are due to significant compressive residual stresses in a superficial layer of the material. The present study provides a reference for improving the mechanical properties of AISI D2 steel by laser shock peening.

A constitutive model for the uniaxial tensile plastic behavior of metals based on the instantaneous strain-hardening exponent

The present work develops a new constitutive equation model for strain-hardening behavior of metallic materials (named herein as the Gonoring model) based on the definition of the instantaneous strain-hardening exponent. This new proposal was applied to experimental uniaxial tensile data of a lean duplex stainless steel alloy UNS s32304 (LDSS 2304) in the as-received (AR) condition and on identical heat-treated specimens at four different temperatures. This choice was justified because this is a steel that presents two phases (ferrite and austenite), which makes it a more universal example from the point of view of applying a new constitutive equation model. These heat treatments induced sigmoidal strain-hardening behavior at uniaxial tensile in this alloy. The Gonoring proposal was able to predict the strain-hardening behavior of both the sigmoidal and parabolic-shaped strain-hardening curve of a lean duplex stainless steel alloy 2304.

A novel approach combining grain boundary engineering and grain boundary serration to enhance high-temperature hot corrosion resistance in Alloy 617

In this work, a novel idea of combining two established microstructural engineering approaches viz., grain boundary engineering (GBE) and grain boundary serration (GBS) through optimization of thermomechanical and thermal processing in Alloy 617 is investigated and the superior resistance of GBE+GBS microstructure to the high-temperature hot corrosion is demonstrated. To achieve the GBE+GBS microstructure, the GBS treatment was introduced as a part of the GBE processing schedule (i.e., incomplete GBE+GBS) and following the GBE treatment (i.e., complete GBE+GBS). The extent of GBS is found to be similar in all the processed specimens. However, the extent of GBE is observed to be lower in the specimens undergoing incomplete GBE+GBS. This is due to the occurrence of recrystallization and consequent infrequent multiple twinning. On the other hand, a higher extent of GBE is achieved in the specimens subjected to complete GBE+GBS owing to the retention of the optimized GBE microstructure following the GBS treatment. The synergistic influence of GBE and GBS on the hot corrosion behavior is assessed by exposing the as-received (AR) as well as optimized grain boundary engineered and serrated (GBES) specimens to a salt mixture at 1273 K. The percolation depth after 24h and 48h exposure is significantly lower in the GBES specimen (∼55 µm and ∼115 µm, respectively) than the AR condition (∼305 µm and ∼630 µm, respectively). This is ascribed to the incorporation of Σ3n (n ≤3) and serrated boundaries in the GBES microstructure which obstructed the infiltration of harmful species into the alloy.