Drop In Hardness Research Articles

Effect of thermal exposure on the microstructure and mechanical behaviour of high-chromium steel studied using sub-sized specimens

Creep-resistant steel are one of the critical materials for the energetic industry. Increasing the creep resistance up to 650 °C is one of the high-priority tasks in the material science. Another important issue is a problematics of residual lifetime assessment. The residual lifetime is tied to microstructure development or mechanical property development, which can be measured during the lifetime. This paper deals with thermal exposure of experimental nitrogen-free steels, promising potential use up to the temperature 650 °C. Both mechanical properties and microstructure evolution were followed during exposure at 650 °C for as long as 5000 h. Mechanical properties were measured at the exposure temperature (by tensile testing) and also at room temperature (hardness measurement). A strong correlation was found between the high-temperature tensile strength and the room temperature hardness. The tensile strength dropped by 56 MPa or 29 MPa for the experimental steel during the 500 h exposure and this decrease was closely followed by the drop in hardness. This correlation opens way for a small-scale sample extraction, intended only for a metallography and harness measurement. Such change of analysis method would significantly reduce required sample dimensions by an order of magnitude comparing with a sample intended for miniaturized tensile tests or a small-punch testing.

Modification of mechanical and microstructural characteristics into Ti‐6Al‐4V alloy by thermal treatment

Purpose The purpose of this study is to analyze the titanium alloy under heat treated condition. Titanium alloy heat treatment, particularly Ti‐6Al‐4V alloy, has been an important field of study due to its wide variety of uses in the aerospace, automotive, and biomedical sectors. The mechanical characteristics of titanium alloys are heavily influenced by their microstructure. Cold‐rolled Ti‐alloys have strong bending and tensile strength due to extensive β‐phase precipitation on the α matrix. However, various heat treatment (HT) methods can affect the mechanical characteristics. The current study seeks to investigate the effects of various heat treatment procedures on the microstructural and mechanical changes of Ti‐6Al‐4V alloy, in order to achieve an optimal balance of strength, hardness, and ductility for a variety of real-world applications. Design/methodology/approach Three plates of Ti‐6Al‐4V alloy were heated above the β‐transus temperature for a certain period and then cooled via furnace, air, and sand. One extra plate was kept in ‘untreated’ condition and given name ‘as received’ plate. The three heat treated plates were evaluated and compared with ‘as received’ plate based on tensile strength, bending strength, hardness, and microstructural changes. Findings A considerable change in orientation of α and β was noted through optical microscopy upon heat treatment. The mechanical testing revealed that all the cooling methods adopted in the study have reduced the UTS and increased the YS of the plates. The ductility of the alloy was primarily enhanced by 'air cooling' and 'sand cooling' methods. Originality/value Notably, the hardness test findings indicated a significant drop in hardness for the ‘sand‐cooled’ sample. Furthermore, the ‘air cooled’ sample showed the maximum hardness due to the production of acicular α regions.

Microstructural insights into the coarse-grained heat-affected zone of a high-strength all-weld metal: Development of a continuous cooling transformation diagram

AbstractThe present study deals with the development of a continuous cooling transformation diagram corresponding to the coarse-grained heat-affected zone of a high-strength all-weld metal with a minimum yield strength of 1100 MPa fabricated via gas metal arc welding. Dilatometry tests were conducted to determine the transition temperatures. High-resolution imaging methods, such as transmission electron microscopy and atom probe tomography, as well as nanoindentation, were employed to resolve the microstructural constituents. At fast cooling rates (t8/5 from 1.4 to 25 s), the microstructure comprises a mixture of martensite and coalesced bainite, with a slight increase in the content of coalesced bainite with faster cooling. This demonstrates that coalesced bainite cannot be avoided in the coarse-grained heat-affected zone of the current alloy by increasing the cooling rate. With slower cooling (t8/5 ≥ 50 s), the microstructure becomes increasingly bainitic, accompanied by a marginal drop in Vickers hardness. At t8/5 times of 500 s and 1000 s, the all-weld metal consists of granular bainite with significant amounts of retained austenite and different shaped martensite-austenite constituents. The coarser massive-type constituents contain body-centered cubic grains, sized in the hundreds of nanometers, with a hardness approximately twice as high as that of the surrounding bainitic matrix.

Impact of cold fluid injection on caprock integrity

In Brazilian pre-salt fields, the extracted carbon dioxide (CO2) is reinjected with lower temperatures into the reservoirs to maintain reservoir pressure, improve oil recovery and reduce greenhouse gas emissions. The cold CO2 injection can alter the mechanical and hydraulic properties of the subsurface and induce variations in formation stresses. Stress changes can be sufficiently high to generate undesirable fracture propagation, damage the caprock, and activate natural fractures or geological faults. Consequently, they can induce seismicity, leaks, and contamination of shallower aquifers and CO2 release into the atmosphere. This work investigates the thermo-hydro-mechanical effect of cold fluid injection on caprock integrity. To this end, a fully coupled thermo-hydro-mechanical (THM) finite element model governs the rock formation behavior. The proposed model considers poroelasticity, fluid flow, and convection/diffusion heat transfer within the permeable rock formation under single-phase fluid flow conditions. The temperature diffusion, pore-pressure buildup, and stress variation under isothermal or non-isothermal injection scenarios are investigated. The results show reservoir expansion in the isothermal scenario due to fluid injection, which is expected in the pressurization process. In the non-isothermal scenario, the thermally disturbed region throughout the reservoir resulted in compaction rather than expansion, even though it was subjected to injection. The instantaneous drop in temperature induces a hard drop in pore pressure and plastic deformations in the reservoir. The lower interval of the caprock presents critical horizontal tension stresses compromising its integrity. Finally, the study adds valuable insight to better understand the complex cold fluid injection process, considering hydraulic, mechanical, and thermal coupling.

Investigation of softening in hardfaced layers during welding

Hardfacing is a widely used technique to create wear-resistant layer on the base material to ensure good durability and performance under harsh operating conditions. However, despite its effectiveness in improving wear resistance, hardfaced layers can sometimes exhibit softening phenomena during welding, compromising their mechanical properties and overall performance. In this research, the effect of heat input was investigated in case of Fe-based hardfacing material with high Cr content. 4 different heat inputs were applied with gas metal arc welding and significant differences were determined in hardnesses, which can be influential to the lifetime of hardfaced parts. Hardness drop happens in the heat-affected zones between the hardfaced layers and the highest heat input causing the most significant softening (20% hardness drop).

Effect of Yb3+ on the thermophysical and mechanical properties of gadolinium zirconate ceramics: First-principles calculations and experimental study

Thermal barrier coating materials require high phase stability, low thermal conductivity, and a thermal expansion coefficient that matches the bonding layer. Cation doping is a highly efficient method for enhancing the thermophysical and mechanical characteristics of materials used in thermal barrier coatings. The thermophysical and mechanical properties, as well as the phase stability at high temperatures of ceramic materials doped with Yb3+ in gadolinium zirconate, are examined by utilizing first principles calculations and solid-state reaction methods. As the Yb3+ content increases, the grain average particle size of gadolinium zirconate ceramics first decreases and then increases. Given that a smaller grain size results in more grain boundaries, thereby reducing the thermal conductivity of the material, it can be inferred that Yb0.20 ((Gd0.8Yb0.2)2Zr2O7) with the smallest grain size exhibits lower thermal conductivity. As the Yb3+ content increases, both the calculated and experiment results suggest the Young’s modulus of gadolinium zirconate initially declines to its minimum value when the Yb3+ content is 0.5 and subsequently experiences a little increase. Furthermore, as the concentration of Yb3+ increases, the material initially experiences a drop in both hardness and fracture toughness, followed by a subsequent increase. Both the calculation and experimental results indicate that the thermal conductivity of gadolinium zirconate initially decreases and then increases. Among the different compositions, Gd1.5Yb0.5Zr2O7 demonstrates the minimum thermal conductivity, measuring 1.029 W/(m⸱K) according to the Clark model and 1.152 W/(m⸱K) according to the Cahill model. At a temperature of 1273 K, the experimental results demonstrated that (Gd0.8Yb0.2)2Zr2O7 has the lowest thermal conductivity of 1.415 W/(m·K). Furthermore, both the calculated and experimental thermal expansion coefficients of the material decrease first until the Yb3+ concentration is 0.5 and then increase slightly when the Yb3+ content increases. Moreover, gadolinium zirconate ceramics have demonstrated a consistent single-phase fluorite structure, excellent stability at high temperatures, and remarkable structural integrity during repeated heating and cooling cycles. The calculation results exhibit strong congruence with the experimental data. The objective of this work is to improve the thermophysical and mechanical properties of gadolinium zirconate ceramics for their application as materials for thermal barrier coatings.

Process parameter translation strategies for variable directed energy deposition spot size using 316L, copper, and Inconel 625

Directed energy deposition (DED) is a form of additive manufacturing available across a variety of laser spot diameter values, often referred to as spot sizes. However, there is no method to easily transfer process parameters across discrete spot sizes, leading to DED process parameters that are equipment specific and not widely applicable. In this study, a strategy is proposed and investigated for five spot sizes that keep the areal energy density constant while varying power, feed rate, and powder flow during the deposition of 316L stainless steel. An assessment of trends in hardness and microstructure is possible due to the novel production of components of a single material across several spot sizes using a single nozzle on a single DED system. The proposed strategy was used to nullify the hardness drop during functional grading of Inconel 625 and pure copper, enabling fabrication of multi-material sample that does not compromise desirable properties. This application shows the value in establishing more efficient process parameter development and understanding spot size influences on geometric and material property flexibility, to enable a more diverse powder-based DED design space and to increase the industry adoption of DED systems.

Dilution induced variation of microstructure and mechanical properties on Co-Cr-Fe-Ni high entropy alloy coatings prepared by laser cladding

The remarkable properties of some series of high entropy alloys (HEAs) have garnered extensive interest in the development of HEA coatings. In this study, we prepared non-equiatomic Co-Cr-Fe-Ni HEA coatings using laser cladding method with Co-Cr-Fe-Ni cable-type welding wire (CTWW) as the filling material and investigated the effect of dilution rate on the microstructure evolution of coatings. By changing the wire feeding speed, a large dilution rate range was obtained which is from over 80 % to below 20 % and a variation of the coating's microstructure and mechanical properties was discovered within this large dilution rate range. All of the coatings are dense and uniform, with good metallurgical bonding. A pivotal discovery was made when the dilution rate decreased from approximately 35 %–40 % to below this threshold. The coating transitions from face centered cubic (FCC) and body centered cubic (BCC) dual-phase to FCC single-phase, accompanied by a precipitous drop in hardness from approximately 425 HV to below 175 HV. The interlaced distribution and dislocation pile-up of the layered BCC eutectic structure within the FCC phase are the main reasons for this dramatic change. Therefore, controlling the dilution rate is an effective way to regulate the performance of Co-Cr-Fe-Ni HEA coatings.

The effects of heat treatment on the mechanical properties of 450 HB wear resistant steel

The effects of heat treatment on the mechanical properties of 450 HB wear resistant steel produced by Usiminas steelworks in the form of heavy plates were investigated. The results showed that when tempering temperature is lower than 200°C, there are no significant changes in hardness, tensile properties and absorbed energy in Charpy V-notch test. With further increase in temperature up to 400°C, hardness, tensile strength, total elongation and impact toughness exhibited a slight downward trend. For heating carried out from 400°C to 600°C, a very significant drop in hardness and tensile strength and an increase in total elongation and absorbed energy values were observed. The abrasive wear resistance, evaluated by dry-sand rubber wheel test, increased with the heating up to 500°C. With the additional rise in temperature to 600°C, the abrasive wear resistance decreased, reaching a similar level to the reference state (steel in as-delivered condition).

Failure of dissimilar QP980/DP600 advanced high strength steels resistance spot welds

This study investigates the microstructure, failure characteristics, and mechanical properties of dissimilar resistance spot welds between QP980 quenching and partitioning steel and DP600 dual phase steel. The dissimilar spot welds exhibited a heterogeneous microstructure, with a fusion zone predominantly composed of martensite, significantly overmatching both base materials. A fully martensitic structure with grain size gradient was observed in the upper-critical heat affected zone (UCHAZ) on both sides of the dissimilar joint. In the sub-critical heat affected zone (SCHAZ), no significant phase transformation occurred on both sides. However, at high welding currents, a slight tempering of pre-existing martensite was detected on the QP980 side resulting in a minor hardness drop in this zone. There was a critical welding current at which the failure mode was changed from interfacial mode to pullout mode. The dissimilar QP/DP joint showed a lower tendency to fail via interfacial failure mode compared to similar QP/QP and DP/DP joints, attributed to a higher fusion zone hardness overmatching factor and greater nugget rotation. Pullout failure of dissimilar QP/DP combination was assessed in detail through interrupted tensile shear test. It was found that failure at stronger QP980 side occurred by ductile cracking mechanism initiated from the notch tip, while failure at softer DP600 side occurred by through-thickness localized necking. The former was found to be the prior failure mechanism controlling the load bearing capacity of the dissimilar joint. The mechanical properties of dissimilar QP/DP joints were discussed in terms of peak load and energy absorption, and then were compared to those of similar DP/DP and QP/QP joints in the light of weld microstructure and failure mechanisms.

Comparison of Softening Behavior and Abrasive Wear Resistance between Conventionally and Additively Manufactured Tool Steels

Directed energy deposition (DED) is a powerful method for hard‐facing the existing tool components. Herein, three tool steel grades including a newly developed maraging steel (NMS), a cold work tool steel (V4E), and a high boron steel (HBS) are cladded on a hot work tool steel substrate. After tempering, the cladded tool steels are exposed to high temperatures at 600, 700, and 800 °C for 3 h to evaluate their softening resistance. The results show that all three tool steel grades have a significant hardness drop when the softening temperature reaches 700 °C. The investigated NMS has the lowest initial hardness in the tempered state but the best softening resistance. In contrast, HBS has the highest initial hardness but the worst softening resistance among the three steel grades. V4E tool steel has a moderate softening resistance compared to the other two steel grades. The factors contributing to the softening resistance have been discussed. Corresponding conventional tool steels are also adapted as references for comparison. Except for the NMS, the additive manufacturing tool steel samples have a better softening resistance than the conventional counterparts owing to more alloying elements trapped in the matrix. The abrasive wear resistance of the tempered and softened tool steels manufactured by DED and conventional methods is also evaluated and the wear mechanism is discussed. Besides the hardness, the free spacing λ between coarse hard particles is one of the major factors influencing the abrasive wear resistance.

Effect of Co-Surfactants on Properties and Bactericidal Activity of Cu2O and Hybrid Cu2O/Ag Particles.

Nanomaterials based on metal oxides, especially Cu2O, have received much attention in recent years due to the many unique properties of the surface plasmon resonance they provide. The report presented the co-precipitation method, a simple preparation method to produce Cu2O oxide particles. In addition, to improve the unique antibacterial properties of Cu2O, a proposed method is to attach Ag nanoparticles to the surface of Cu2O particles. The Cu2O and Cu2O-Ag particles were synthesized based on redox reactions using ascorbic acid (LAA) as a reducing agent. Moreover, in this experiment, two surfactants, polyethylene glycol 6000 (PEG 6000) and sodium dodecyl sulfate (SDS), were added during the manufacturing process to create particle samples and particle combinations with better properties than the original sample. Changes in the characteristics and properties of particle samples are determined by many different physical and chemical methods such as ultraviolet-visible spectroscopy (UV-Vis), infrared spectroscopy (IR), noise X-ray radiation (XRD), scanning electron microscope (SEM), dynamic light scattering (DLS), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). Finally, the activity against bacteria, including E. coli and S. aureus, was also tested using the agar well diffusion method to determine the zone of inhibition. The results improved the particle size value, which decreased by half to 200 nm when two additional surfactants, PEG and SDS, were added. In addition, the antibacterial ability has also been shown to increase significantly when the diameter of the bacterial inhibition zone increased significantly, reaching values of 20 mm (Cu2O/Ag/SDS) and 32 mm (Cu2O/Ag/PEG) for the E. coli bacterial strain. The initial test sample was only about 14 mm in size. The S. aureus bacterial strain also had a similar improvement trend after adding Ag to the Cu2O surface with the appearance of two surfactants, SDS and PEG. The inhibition zone diameter values reached the optimal value at 36 mm in the Cu2O/Ag/PEG particle combination sample compared to only the initial 26 mm in the Cu2O particle sample. Finally, the particle samples are added to the acrylic emulsion paint film to evaluate the changes. Positive results were obtained, such as improvement in adhesion (1.22 MPa), relative hardness (240/425), and sand drop resistance (100 L/mil) in the Cu2O/Ag/PEG particle combination sample, which showed the correctness and accuracy of the research.

The influence of natural aging on the precipitation behavior of the low-alloy content Al-Zn-Mg aluminum alloys during subsequent artificial aging and related mechanisms

The age hardening and precipitation behavior of the low-alloy content and widely used Al-Zn-Mg alloy during artificial aging was studied adopting methods of Vickers hardness testing and transmission electron microscopy. To meet with practical application of the production line conditions, the influence of natural aging (NA, at room temperature) on the precipitation behavior during subsequent artificial aging (AA, at 130 °C∼150 °C) and related mechanisms are discussed based on the classical nucleation theory. The results show that precipitates like solute clusters and GP zones will form during the NA process, which have a significant influence on the subsequent precipitation behavior during AA. These NA precipitates will dissolve at the initial stage of AA resulting in abundant localized supersaturated regions which are the favorable nucleation sites for η′ phase. This positive effect is highly dependent on the temperature adopted during the AA process and the duration of NA. Higher AA temperatures result in a more noticeable increase in hardness compared to the samples without NA but require a longer duration of AA to achieve a relatively high and stable peak-aging hardness. However, an excessive long NA period can lead to a significant drop in hardness in the over-aging status. In the low-alloy content Al-Zn-Mg alloys, the actual nucleation rates of precipitation during the early stages of AA vary significantly with the AA temperature, which serves as the underlying cause of the observed NA effect. These results provide rather an important guidance for the production process of the 7003alloy and other aluminum alloys with similar chemical composition.

The response of 316 L steel manufactured by selective laser melting route to high-temperature oxidation behaviour: The role of microstructure modification

The current work examines the effect of 316 L steel's microstructure, which is modified through varying scanning angles with the sample surface (HNS (0°), INS (45°), and VNS (90°)) in the selective laser melting (SLM) method and through surface mechanical attrition treatment (SMAT), on its high-temperature oxidation behaviour (at 600–800 °C) is investigated. We have obtained a deeper understanding of the steel's oxidation behaviour by applying various characterisation techniques. The SMATed steel has a ∼ 1000 μm thick deformed layer containing a gradient microstructure, and its topmost layer contains fine twins and nanograins (∼30 nm). The hardness of this surface is ∼1.65 times the non-treated steel's hardness. All samples follow a parabolic rate law during oxidation. The VNS sample unveils the slowest oxidation rate amid the non-treated samples. SMAT increases the activation energy of oxidation. The distribution of elements across the oxidised samples' cross-section shows discontinuous Cr spreading within the oxide layer on the non-treated samples; however, the deformed samples show uniform distribution. Unlike non-SMATed samples, a minute decline in Cr and Mn content is observed underneath the oxide layer on the SMATed samples, confirming their enhanced outward diffusion. The oxide layer on SMATed samples has more Cr- and Mn-rich oxides. These oxides occupy the grain boundaries of the oxidised non-SMATed surfaces, where the micro-pores and cracks are present. Conversely, oxidised SMATed surfaces display uniform, defect-free Cr- and Mn-rich oxides with finer grains. Moreover, the SMATed layer remains reasonably stable during high-temperature oxidation (hardness drop ranges between ∼9 and ∼ 30%).

Effect of high temperature annealing on the microstructure evolution and hardness behavior of the Inconel 625 superalloy additively manufactured by laser powder bed fusion

Additive manufacturing of Inconel 625 components attracts great interest due to its ability to produce parts with complex geometries that are needed for high-temperature applications in the aerospace, energy, automotive and chemical industries. To take full advantage of the potential of additive manufacturing, an in-depth understanding of the effects of prolonged high-temperature annealing on microstructure and hardness evolution is needed. Previous research in this field has mainly focused on a limited range of temperature and time. This study aims to determine the effect of prolonged high-temperature annealing on the evolution of intermetallic phases and carbides, as well as changes in the dislocation substructure of Inconel 625 superalloy additively manufactured by laser powder bed fusion subjected to stress relief annealing and subsequent isothermal annealing at a temperature up to 800 °C for 5–500 h. The microstructure development is correlated with hardness behaviour. It is determined that the microstructure evolution proceeds in four stages with temperature and time increase. In the initial stress-relieved condition, a cellular microstructure with nano-sized precipitates of the Laves phase and NbC carbides at the cell walls occurs, and hardness is equal to 300 HV10. In the 1st stage of the microstructure evolution, the γ'' phase particles precipitate on the cell walls, which results in hardening up to 383 HV10 in the specimen annealed at 700 °C for 5 h. The 2nd stage involves the precipitation of the γ'' phase both on the cell walls and inside the cells, as well as the formation of dislocation networks, which contribute to the softening effect and hardness drop to 319 HV10. In the 3rd stage, at temperature 700 and 800 °C, the δ phase, M23C6 carbides, and the Laves phase precipitate and grow, and the subgrain boundaries are formed. The hardness is in the range of 340–350 HV10 and is higher than in the 2nd stage. In the 4th stage, as the annealing time is increased at a temperature of 800 °C, the δ phase and M23C6 carbides coagulate, and the Laves phase particles spheroidize or partially dissolve. Very intense precipitation and growth of the hard δ phase particles provide an increase in hardness to 402 HV10. As a result of systematic studies, the various strengthening and softening mechanisms acting during high-temperature annealing are determined.Graphical abstract

A combination of aluminium strip and brass mesh to process a refined structure composite via accumulative roll bonding: A characterization study

In the present study, a dissimilar composite consisting of commercially pure aluminium and 70–30 brass alloy was manufactured using the accumulative roll bonding process. For microstructural evaluations, optical microscopy, scanning electron microscopy, and electron back-scattered diffraction were employed. It is indicated that after the 3rd ARB pass, the bonding between the reinforcements and matrix strengthened. However, after the 5th pass, the formation of micro-cracks along the Al/brass interface was observed. These cracks accompanied by the separation of matrix/particle led to fracture of the composite from the base metal as confirmed by fractography of the failed specimen. Also, the average diameter of Al grains was estimated to range from 1.2 μm (between brass particles) to 850 nm (near brass fragments). The micro-texture study of the selected areas indicated the evolution of P and Q components known as recrystallization texture near the brass particles. Above all, mechanical evaluations were conducted using Vickers microhardness and tensile tests. Results revealed a dramatic increase in the composite ultimate strength and hardness and then saturation as compared to that of Al without brass fragments. However, a sudden drop in hardness occurred for the composite at the 3rd pass.

Direct aging of additively manufactured A20X aluminum alloy

This study investigates the effect of direct aging on a newly developed high-performance aluminum alloy A20X for laser powder bed fusion. Three different temperatures (180 °C, 200 °C, and 220 °C) and nine different heat treatment durations (5 min to 30 h) were considered. The material exhibited significant softening (up to 23.7 % hardness drop) after direct aging. The extent of softening was proportional to the temperature and duration of heat treatment. During direct aging, incoherent Al2Cu (θ) precipitates ({110}θ ǁ {220}Al) coarsened and the volume fraction remained constant (4.52–4.63 %). The average precipitate size grew by up to ∼100 % through direct aging and no metastable precipitates (such as θ′ or Ω) formed, suggesting the absence of supersaturated matrix in as-printed A20X. Accordingly, the yield and tensile strengths of the alloy dropped by up to 27 % and 19.4 %, respectively. The continuous Mg/Ag solute wall observed at grain boundaries in the as-printed state caused serrated plastic flow due to the locking/unlocking of dislocations. Longer aging treatments generated discrete solute co-clusters along the grain boundaries and TiB2/Al interface promoting smoother plastic flow.

Sliding wear behaviour of conventional and cryotreated PM Cr-V (Vanadis 6) ledeburitic tool steel

Cryogenic treatment is a widely accepted method for extending the tool life of tool steels. This study focuses on investigating the tribological properties of PM Cr-V cold work tool steel subjected to conventional and cryogenic treatments. The aim of the study is to compare the reciprocal sliding wear performance of Cr-V cold work tool steel under different treatment conditions. The Cr-V tool steel specimens were cryotreated at temperatures of −75 °C, −140 °C, or −196 °C, followed by double tempering at 170 °C or 530 °C for 2 h. Cryotreated specimens exhibited a 10% increase in hardness compared to conventionally treated specimens after tempering at 170 °C. However, specimens cryotreated and tempered at 530 °C showed a 7% drop in hardness. Reciprocating sliding wear tests were conducted at room temperature using an Al2O3 ball as the counter-body to simulate abrasive wear. The results indicate that the friction coefficient is primarily influenced by the applied load and sliding velocity rather than the material treatment. Cryogenic treatment at 170 °C improved the wear performance by approximately 24% compared to conventionally treated specimens, while cryotreated specimens tempered at 530 °C did not exhibit any improvement in wear performance compared to conventionally treated specimens.

Investigation of Recrystallization Kinetics in 1050 Al Alloy by Experimental Evidence and Modeling Approach.

The recrystallization (RX) kinetics of commercially pure Al alloy is studied under the scope of annealing temperature, time, and degree of deformation. To examine the distribution of recrystallization, Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory is employed, where the path of microstructural transformation from the deformed state to the fully recovered one is studied as a function of the volume fraction of recrystallized grains (XV) and annealing time. The drop in hardness is recorded for the samples at various stages of annealing with a corresponding decrease in stored energy as the annealing time increases. The stored energy obtained from the hardness results and Orientation Imaging Microscopy (OIM)-based method is found to be in good agreement with each other, proving the efficiency of both techniques. To determine the volume fraction of the recrystallized microstructure, data obtained from Vickers hardness measurements are used. Various parameters associated with recrystallization statistics such as the critical radius of nuclei, the incubation period, and the mobility of High-Angle Grain Boundaries (HAGB) were derived from the experimental evidence. The experimental data also suggest a sharp drop in the velocity of HAGB as the RX transformation process approaches its completion, which is found to be a direct result of a drop in stored energy. A softening window between 42 s and 55 s is identified for our experimental data where the hardness, stored energy, and velocity of HAGB drops very sharply, and the maximum fraction of deformed grains is expected to be converted to the recrystallized ones. Along with experimental observations, an analytical model was developed, which helps to approximate the kinetics of RX and corresponding parameters for various annealing temperatures and strains while revealing the characteristic feature of Avrami exponent n. Both experimental evidence and model data reveal a very strong dependency of recrystallization behavior on the stored energy.

Evaluation of Struthiocamelus eggshell as an in vitro alternative to extracted human teeth in preliminary screening studies on dental erosion.

This in vitro work investigates the potential of ostrich eggshellas a substitute for extracted human teeth in preliminary screening studies on dental erosion. Additionally, it aims to demonstrate the potential of ostrich eggshell compared to human enamel in evaluating the efficacy of a preventive agent in protecting against dental erosion, using an artificial mouth model. The experiment utilized 96 erosion testing specimens from each substrate, human enamel, and ostrich eggshell. The specimens were subjected to six different experimental regimens of increasing erosive challenge, simulating the consumption of an acidic drink. The acidic drink was delivered at a consistent volume and duration range. Both artificially stimulated and unstimulated saliva flowed throughout the experimental regimens. Surface hardness was measured using a Through-Indenter Viewing hardness tester with a Vickers diamond, while surface profiling was done using a surface contacting profilometer with a diamond stylus. An automated chemistry analyzer system was used to detect calcium and phosphate ions. The study found that ostrich eggshell specimens demonstrated predictable surface loss, hardness drop, and ion loss due to the acidic challenge. Meanwhile, enamel appeared to fall short in terms of surface hardness predictability. The transient hardness loss phase, which manifests as an overlooked decrease in surface hardness despite significant ion and structural loss, may explain this phenomenon. The experiment showed that assessing surface loss is essential in addition to hardness testing, particularly as certain experimental conditions may produce a false perception of tissue recovery despite the actual surface loss. By analyzing the response of ostrich eggshell specimens to erosive challenges, researchers were able to identify an "overlooked" reduction in hardness in enamel specimens. The differences in the structure, chemical composition, and biological response to erosion in the presence of artificial saliva between enamel and ostrich eggshell could explain their distinct behaviors.