Orowan Strengthening Mechanism Research Articles

Effect of Deep Cryogenic Aging Treatment on Microstructure and Mechanical Properties of Selective Laser-Melted AlSi10Mg Alloy

Deep cryogenic aging (DCA) is a newly developed heat treatment technique for additive-manufactured metallic materials to reduce residual stress and improve their mechanical properties. In this study, AlSi10Mg alloy samples fabricated by selective laser melting were deep-cryogenic-treated at −160 °C and subsequently aged at 160 °C. Phase and microstructural analyses were conducted using X-ray diffraction, optical microscopy, scanning electron microscopy, and transmission electron microscopy, while the mechanical properties were evaluated through microhardness and tensile testing at room temperature. The results indicated that the DCA treatment did not have an effect on the morphology of the melt pools. However, it facilitated the formation of atomic clusters and nanoscale Si and β′ phases, as well as accelerating the coarsening of grains and the ripening of the eutectic Si phase. After DCA treatment, the mass fraction of the Si phase experienced an increase from 4.4% to 7.2%. Concurrently, the volume fraction of the precipitated secondary phases elevated to 5.1%. The microhardness was enhanced to 147 HV, and the ultimate tensile strength and yield strength achieved 495 MPa and 345 MPa, respectively, with an elongation of 7.5%. In comparison to the as-built specimen, the microhardness, ultimate tensile strength, and yield strength increased by 11.4%, 3.1%, and 19.0%, respectively. The improvement in mechanical properties is primarily attributed to the Orowan strengthening mechanism induced by the secondary phases.

Microstructural evolution and mechanisms affecting the mechanical properties of wire arc additively manufactured Al-Zn-Mg-Cu alloy reinforced with high-entropy alloy particles

The mechanical properties of Al-Zn-Mg-Cu alloys produced via wire arc additive manufacturing (WAAM) are often weakened by the presence of continuous and coarse precipitated phases, which significantly limits their practical applications. In this study, high-entropy alloy (HEA) particles were incorporated into Al-Zn-Mg-Cu alloy during the WAAM process, which inhibits the continuity of precipitated phase, and the mechanism of microstructure evolution and macroscopic mechanical properties optimization of the components are explored. The results show that HEA particles promote grain refinement, and disrupt the formation of continuous precipitated phase along the grain boundary by generating plenty of fine spot-like precipitated phases, thus inhibiting grain boundary segregation. The spot-like precipitated phases are connected via a slender second-phase-band. The primary precipitates include the metastable η', stable η, and T phases, and the diffusion of solute atoms forms the Al3Ni and Al3(Ni, Cu)2 phases. The tensile strength increases from 247.4±5.9 MPa to 326.2±19.7 MPa in the horizontal direction and from 273.0±13.7 MPa to 335.4±11.1 MPa in the vertical direction, which correspond to increases of 31.9 % and 22.9 % respectively. The enhancement of mechanical properties is mainly attributed to Hall-Petch, Orowan, load-transfer, solid-solution and dislocation strengthening mechanisms. Only slight variation occurred in the elongation, the increased number of fine spot-like precipitated phases and grain boundaries hinder the crack propagation, while the increased number of pores facilitates the crack propagation, and these effects almost balance each other out in competition. These findings are expected to provide new insights into the microstructure optimization of WAAM components, thereby meeting more practical applications.

Development and tribological investigation of B4C reinforced AA5082 Aluminum alloy cast composites for automotive applications

In this work, AA5082 alloy is used as base alloy to fabricate aluminum composites using fine reinforced particles of boron carbide (B4C). The conventional method of stir casting is employed for the production of composites. The particles are used with varying weight % of 5, 10, 15 and 20 for the composite fabrication. The microstructures of the composites are examined using the Scanning Electron Microscopy and x-ray Diffraction patterns. The hardness of the composites is tested and found to increase from 73 HV in base alloy to 93 HV in the AA5082 composite having B4C proportion of 15%. However, a slight decrease in hardness is also observed at higher wt% of B4C which could be due to agglomeration of particles. Evaluation of yield strength showed an escalation in the strong point with the addition of reinforced particles under the effect of orowan strengthening mechanism. Wear analysis conducted on Tribometer indicates that the escalation of load and sliding distance is proportional to the loss of material in composites whereas, wear declined with the rise of sliding speed. The micrograph examination of the wear tracks reveals the material removal mechanism from the composite as abrasive in nature. Pitting at certain places is also observed.

The role of the post-heat treatment on the Cr-based precipitates and related room temperature mechanical properties of the sintered Nb-lean Cu–Cr–Nb alloy

Nb-lean Cu–Cr–Nb alloys have been widely applied in electrical industries as the structural conductive material owing to their excellent combination of the mechanical and electrical properties at room temperature. In this work, the influence of temperature during fast sintering and post-heat treatment strategies on the precipitate evolution and room temperature mechanical properties of the Cu–3Cr-0.5Nb (wt.%) alloy was investigated. The increasing sintering temperature will improve the density and mechanical properties of the alloy without any obvious grain growth during this non-equilibrium process, while the post-aging at lower and higher temperatures can effectively control the formation and coarsening process of the Cr-based precipitates. Systematic characterization was then conducted on the microstructural evolution, especially the altering precipitates’ size and distribution, in the alloy at both as-sintered and the aged conditions, which is correlated to its room temperature tensile properties. Lower aging temperature will induce the nucleation of the new Cr2Nb precipitates without causing a significant coarsening of the existing precipitates like aging at higher temperature. Therefore, the low-temp. aged sample exhibits the highest tensile strength and elongation due to the enhanced Orowan strengthening mechanism induced by its unique precipitate microstructure.

Orowan strengthening with consideration of thermal activation

Orowan strengthening is a key strengthening method for metallic materials. However, a debate still exists on the effect of temperature on the Orowan strengthening mechanism. Herein, the effect of temperature on the Orowan strengthening mechanism is systematically investigated, an Orowan strengthening mechanism with thermal activation is developed, and the corresponding Orowan stress is deduced. The results indicate that the precipitate scales substantially affect the thermal activation–based dislocation that bypasses the precipitate processes. In small precipitate scales, the thermal activation contribution to Orowan stress cannot be ignored; while in big precipitate scales, the thermal activation contribution can be ignored even at high temperatures. In addition to temperature, the effects of shear modulus, strain rate, and dislocation density on Orowan stress are investigated. This study not only provides new insight into the Orowan strengthening mechanism but also aids in designing new high-temperature structural materials.

Fabrication and strengthening mechanism of crack-free nano-TiC reinforced IN738LC with enhanced mechanical properties by laser powder bed fusion

IN738LC alloy has broad application potential in modern aerospace and energy industries due to its excellent high-temperature durability, excellent corrosion and fatigue resistance, however, its application has been greatly limited due to its high crack sensitivity. To address this challenge, this research proposes a method of incorporating TiC nanoparticles to mitigate cracks and enhance the strength of the nickel-based materials. The crack-free TiC-IN738LC materials were successfully fabricated using laser-powder bed fusion. The relationship between the processing parameters and processed quality was studied. The fracture morphology and mechanical properties of samples were analyzed and the strengthening mechanisms of nano-TiC particles were clarified. The results showed that volume energy density (VED) = 111.1J/mm3 is the optimal processing parameter with the laser energy 225W, scanning speed 750 mm/s, and 0.09 mm hatch distance. The effects of processing parameters were discussed in depth. Compared with the virgin IN738LC, the microhardness of TiC-IN738LC is improved by 20 %–40 %, and the tensile strength of TiC-IN738LC is enhanced by 5%–30 %, respectively, which indicates the significant strengthening effect of nano-TiC on IN738LC. The synergistic effect of fine grain strengthening, load-bearing strengthening and Orowan strengthening mechanisms was accounted for the performance enhancement. The research results provide an experimental reference for selecting the processing parameters of TiC-IN738LC.

Enhancing Tribo-Mechanical and Corrosion Properties of ADC 12 Alloy Composites through Marble Dust Reinforcement by Squeeze Casting Technique.

This research intends to enhance the tribo-mechanical and corrosion properties of ADC 12 alloys by incorporating marble dust (MD) as a reinforcing element. Composites with varied MD concentrations (0-10 wt%) were fabricated using a squeeze casting process, addressing the limitations of conventional casting techniques. The microstructural analysis confirmed homogeneous MD dispersion within the ADC 12 matrix, facilitating an effective load transfer and solid interfacial bonding. As MD content increased, the experimental density decreased, while porosity increased from 1.22% to 3.97%. Remarkably, adding 4 wt% MD yielded a 20.41%, 17.63%, and 15.75% enhancement in hardness, tensile, and compression strength compared to the as-cast ADC 12. Incorporating MD particles facilitated Orowan strengthening and Hall-Petch strengthening mechanisms, contributing to the observed improvements. The wear rate was reduced by 18.33% with MD content, showing a 17.57% corrosion reduction at 72 h. These outcomes establish the synergistic benefits of ADC 12 squeeze casting with MD reinforcement, delivering superior tribo-mechanical and corrosion properties.

Effect Mechanism of Sc Addition and T6 Heat Treatment on Precipitated Phase and Mechanical Properties of Al‐Cu‐Mn Alloy

The microstructure and mechanical properties of cast Al‐Cu‐Mn alloy influenced by various Sc additions (viz. 0.1, 0.2, 0.3, 0.4, and 0.5 wt%) are investigated. It is found that the grain size of α‐Al and the area proportion of the second phase are decreased with the addition of Sc. In addition, the morphology of the precipitated phase in Al‐Cu‐Mn alloy also evolves at different stages, and the solidification temperature range and initial enthalpy change of the alloy are changed, resulting in the formation of a variety of second‐phase containing Sc. Owing to the grain refinement and precipitation strengthening effects, the hardness of as‐cast alloys is better than T6 alloys. Moreover, it is observed that when the Sc content is 0.3%, the mechanical properties of the as‐cast Al‐Cu‐Mn alloy are the minimum, and the Al‐Cu‐Mn alloys after T6 heat treatment are the maximum. These results confirm that the mechanical properties improvement effect of the as‐cast Al‐Cu‐Mn alloy is greater than that of the T6 heat treatment Al‐Cu‐Mn alloy with the addition of Sc. Meanwhile, the Orowan strengthening mechanism is found to have lost its dominant position.

Mechanical and tribological assessment of AA7075 reinforced Si3N4/TaC/Ti hybrid metal matrix composites processed through stir casting process

ABSTRACT In the present research work, microstructural, mechanical and tribological aspects of Aluminium alloy (AA) 7075 reinforced with Titanium (Ti), Tantalum Carbide (TaC), and Silicon Nitride (Si3N4) ceramic particles were explored by utilising stir casting. Mechanical attributes like compression, tensile, hardness and flexural were evaluated. Dry sliding wear experiments at both room (30°C) and elevated atmospheric (60°C & 120°C) conditions were conducted to investigate the wear performances. Microstructural analyses reveal homogeneous distribution of reinforcements in the matrix along with good interfacial bonding with negligible amount of agglomeration. Considering the effect of hard ceramic materials in the matrix alloy tensile, compression, flexural and hardness of the developed MMCs found to be improved when compared with base alloy. Finer grains restrict the dislocation movement due to the Orowan strengthening mechanism of the developed hybrid MMCs. As the force enhances from 20 N to 40 N, the rate of wear for AA7075 reinforced with 0.75 wt% TaC, 6 wt% Si3N4, and1 wt% Ti was found to be minimum. Taguchi and Analysis of Variance (ANOVA) were performed to acquire the optimum process and dominating parameters. Regression analysis showed the relationship between the output and input control factors.

Influence of shoulder diameter on hybrid surface composite of AA7075-T651/SiC/Graphene via friction sir processing

Friction stir processing is a unique method for improving a base metal's microstructure and mechanical properties by adding reinforcement particles. In this study, three different shoulder sizes are used to fabricate the hybrid surface composites AA7075-T651/SiC/Graphene, and the effect of shoulder diameters on composite properties is critically investigated. The optical microscopy technique is used to examine the macro and microstructures of friction stir processed samples. Microhardness and wear tests are used to measure the mechanical and tribological properties of the produced composites. According to recent study work, 21 mm shoulder diameter revealed equiaxed grain microstructure, which is responsible for the increased microhardness and wear. The smaller grain size of 3.2 µm is attained by dynamic recrystallization. The superior microhardness of 194 HV is due to the hall patch relation and the Orowan strengthening mechanism. The decreased COF and wear rate were due to the sample's higher hardness and lubricative behavior of graphene particles.

Effect of boron carbide reinforcement particles on microstructure and mechanical properties of dissimilar friction stir welded aluminum alloys

The current work investigates the role of boron carbide (B4C) reinforcements on the material flow, microstructure and mechanical properties of dissimilar friction stir welded Al5083-6061 aluminum alloys. Four different weld composites were prepared with varying B4C composition (0–4%). The fine B4C particles were added at the adjoining edges by a novel reinforcing technique along the weld line. Optical and scanning electron microscopes were used to study the B4C distribution, dissolution, bonding and fracture regions. The B4C pinned the grain boundaries and the fine grain structure is obtained by preventing the grain growth during the recrystallization process. Mechanism of microstructure evolution in the stir zone with B4C is attributed to dynamic recovery, dynamic recrystallization and particle stimulated nucleation. The highest hardness and strength were obtained in the joint processed with 2% B4C reinforcements. The tensile test results reveal that the weld composite exhibits higher strength not only by decrease in grain size but also due to grain refinement strengthening and orowan strengthening mechanisms which are occurred due to addition of B4C particles.

Mechanical and microstructural behavior of industrial spent catalyst waste and boron carbide reinforced aluminum matrix composites

The concept of reuse and recycling has undergone sustained development in industries to prevent the exhaustion of naturally available resources. The current study is about reusing spent catalyst waste from petroleum refining industries as reinforcement in aluminum composite materials. This work utilized the stir casting method to create nano B4C/waste spent catalyst/Al matrix composites by varying the B4C from 0.5 to 2.0 wt% and maintaining the constant 10 wt% of spent catalyst waste, respectively. Furthermore, the impact of nano B4C and spent catalyst waste on the mechanical and microstructure behavior of aluminum matrix hybrid composites were studied. The compressive strength, hardness, and tensile strength of the aluminum composites obtained with different percentages of nano B4C and spent catalyst waste were enhanced significantly. The increase in tensile strength mainly due to the effect of the Orowan strengthening mechanism and thermal stresses caused by the difference in the CTE of aluminum matrix and reinforcement. The effective mechanical behavior was obtained with 1.5 wt% B4C and 10 wt% spent catalyst waste with massive improvements in hardness (65.62%), compressive (31.81%), and tensile strength (48.23%), respectively, compared to base pure aluminum.

Effect of precipitation evolution of NiAl and Cu nanoparticles on strengthening mechanism of low carbon ultra-high strength seamless tube steel

We report an alloy design strategy, rolling and heat treatment processes for a new low-carbon ultra-high strength seamless tube steel. The evolution of multiphase microstructure and mechanical properties of experimental steel in the rolled, quenched, and quenched-tempered states has been investigated based on the reverse transformation of austenite correlated with the transformation of secondary martensite and co-precipitation behavior. Microstructure observation results show that the microstructure of rolled state is composed of 88.1 ± 0.1% lath bainite (LB) and 11.9 ± 0.1%% granular bainite (GB), the quenched state is composed of 82.1 ± 1.1%% lath martensite (LM) and 17.9 ± 1.1% GB, while the QT steel is composed of tempered martensite (TM) and GB, and the reversed austenite content increases from 0.66 ± 0.03%% at 500 °C to 5.39 ± 0.05%% at 650 °C, and the high reversed austenite content at 650 °C is the basis of secondary martensitic transformation. The co-precipitation sequence of nanoparticles observed by high-resolution transmission electron microscope (HRTEM) is “supersaturated solid solution → B2 NiAl + bcc Cu → B2 NiAl + bcc Cu + B2 core-9R shell → B2 NiAl + fcc Cu”. Aged at 550 °C for 1 h, the experimental steel obtained a maximum yield strength of 1483.5 ± 3.5 MPa, which was attributed to the combined effect of shear and Orowan strengthening mechanisms, and the maximum strengthening increment reached ∼750.5 MPa.

Production and Characterization of Cu/CNT Nanocomposites

In this research, copper nanocomposites reinforced with carbon nanotubes (CNTs) were produced by ultrasonication and conventional sintering, followed by cold rolling. These nanocomposites may be good candidates due to their excellent properties for components in the electrical, electronics, or aerospace industries with highly demanding requirements. The main objectives of this work were to produce and characterize the Cu/CNT nanocomposites, identify the strengthening mechanisms, and study the deformation behavior of the nanocomposites during cold rolling. The nanocomposites exhibited an improvement in hardness and tensile strength of 17 and 67%, respectively, attesting to the strengthening effect of the reinforced material. The yield strength of the nanocomposites was determined considering different mechanisms: (1) load transfer, (2) grain refinement or texture, (3) dislocation, and (4) Orowan strengthening mechanisms. The microstructural and calculated results show that the mechanism that contributes the most to the increase in the properties of the nanocomposite is the load transfer. The nanocomposites show a different texture evolution of the Cu matrix during cold rolling. This can be due to differences in the active slip planes between the matrix and the nanocomposite, which affects the lattice rotation.

Laser powder bed fusion of AlSi10Mg-based composites with graphene and nanodiamond additions

Laser powder bed fusion (LPBF) processing of aluminum matrix composites (AMC) with blends of AlSi10Mg powder and nanodiamond and graphene additives was investigated. AMC with 0.5 wt% nanodiamonds addition was prepared by mechanical mixing, while AMC with 0.5 wt% of multi-layered graphene was prepared by electrochemical deposition. Initial powders for LPBF were thoroughly characterized and optimal LPBF parameters were found based on the relative density analysis and optical microscopy. Processing windows of both AMCs moved towards lower energy density possibly due to the increased total absorptivity of the powders. Raman spectroscopy results, SEM and HRTEM studies of samples after LPBF demonstrated the absence of nano-diamond in the structure after processing which is explained by graphitization of the nanodiamond particles during laser melting. In case of AMC with graphene additives, carbon-containing particles remained in the structure with partial in situ formation of Al4C3, along with a noticeable strengthening effect, which increased material’s microhardness by more than 40% compared to the initial AlSi10Mg alloy. The strengthening effect is explained by the presence of a network of graphene and Al4C3 particles across the solidified melt-pool promoting the Orowan strengthening mechanism.

Mechanical properties of Mg-Gd-Zr alloy by Nd addition combined with hot extrusion

The effect of Nd addition on the microstructure and mechanical properties of as-extruded Mg-9Gd-0.5Zr (wt.%) alloy was investigated. The Mg-9Gd-0.5Zr and Mg-9Gd-2Nd-0.5Zr alloys were extruded at 673 K. The elongated non-dynamic recrystallized (un-DRXed) grains disappear after adding Nd, and uniformly distributed dynamic recrystallized grains with a grain size of 1.68 μm were obtained in the alloy. In addition, numerous nano-Mg5(Gd,Nd) particles were found to precipitate dynamically in the Mg-9Gd-2Nd-0.5Zr alloy, which gave rise to the dynamic recrystallization process via providing nucleation energy through hindering the release of deformation energy and promoting an increase in the strength through the Orowan strengthening mechanism. Moreover, the dynamically recrystallized (DRXed) grains have a weak texture, which plays a significant role in improving the ductility. Therefore, the Nd addition favors the improvement of strength and elongation for the as-extruded Mg-9Gd-0.5Zr alloy, simultaneously.

Improving mechanical properties of copper composite by interconnected MoO2 quantum dots

The strengthening effect of particle-reinforced copper-based composites mainly depends on the interfacial bonding strength and dispersibility of the reinforcement. However, agglomeration of nanoparticles, as a bottleneck, restricts Orowan's strengthening mechanism. Different from the traditional preparation method for stacked nanoparticles, a hydrothermal method was developed to prepare interconnected bridge-like MoO2 quantum dots. Based on the interconnected structure and the brittleness of MoO2, it can be easily broken and uniformly dispersed into copper matrix during the ball milling process. Due to the dispersion strengthening effect and coherence of the interface between MoO2 and copper, these factors improve the mechanical performance of the composite material synergistically, resulting in simultaneous increases in YS (145.76 MPa), UTS (321.67 MPa), and hardness (94.79 Hv). The effectiveness of YS and UTS enhancement is 234% and 41%, respectively, while maintaining appropriate elongation (20.29%) and conductivity (94.9 IACS). MoO2 quantum dots are used for the first time in this work as particle reinforcements, and we demonstrate that the addition of oxide quantum dots to metal matrix composites can significantly enhance the mechanical properties of the composites by changing the morphology of the quantum dots.

Effects of TiB2 particle and local aspect ratio on microstructure and mechanical properties of an I-shaped TiB2/6061Al composite profile

The I-shaped profiles of TiB2/6061Al composite were fabricated by hot pressing sintering and hot extrusion. The effects of TiB2 particle and local aspect ratio on microstructure and mechanical properties were clarified. The results show that TiB2 particles homogeneously distribute in the I-shaped profile. The web and flange of I-shaped profile own different amounts of TiB2 particles, and the web contains more particles than the flange. The interface between TiB2 and Al matrix is in a strong bonding status without defects, and there is a Mg-rich layer accompanied by lots of misfit dislocations around TiB2 particle. The elongated grains in web are significantly narrower than those in flange because of its larger aspect ratio. TiB2 particle promotes the dynamic recrystallization (DRX) during hot extrusion through particle stimulated nucleation mechanism. The DRX fraction of the web is higher than that of the flange due to the higher particle content and larger aspect ratio. The web owns strong brass as well as some weak Dillamore and R textures, while the main textures of flange are A, copper and Dillamore. The addition of TiB2 particles reduces the intensity of main textures but cannot change the types of orientation preference. Adding TiB2 particles and increasing its content enhance the tensile strength and wear resistance through the load transfer, dislocation strengthening and Orowan strengthening mechanisms. The higher DRX fraction and Schmid factor result in higher elongation and lower strength of the web compared to the flange on an I-shaped profile.

Microstructure, superplasticity, and mechanical properties of Al–Mg–Er–Zr alloys

Minor additions of rare-earth elements improve the mechanical properties of aluminum-based alloys due to precipitation strengthening, increased recrystallization resistance, and grain refinement effects. This study investigated the microstructure, room temperature mechanical properties, and superplasticity of Al–Mg–Z–Er alloys with the Mg content in a range of 2.1–4.9 wt%. The alloys' microstructure was presented by an Al-based solid solution matrix enriched with Mg, the (Al,Mg) 3 Er phase of solidification origin, and nanoscale secondary precipitates of the Al 3 (Er,Zr) L1 2 –structured phase. The Al 3 (Er,Zr) precipitates provided the Orowan strengthening mechanism, led to a strong recrystallization resistance and the Zener pinning effect during elevated temperature deformation. An increase of the Mg solute resulted in a solid solution strengthening and facilitated dynamic recrystallization at elevated temperatures. In the alloy with 4.9%Mg, a combined effect of fine L1 2 precipitates, high solute Mg, and (Al,Mg) 3 Er particles led to a fine-grained structure formation and superplasticity with the maximum strain rate sensitivity m of 0.51 and the elongation-to-failure of 550–600% at the constant strain rates of (0.8–1) × 10 −2 s −1 . The mechanical properties at room temperature were studied after the post-deformation annealing of the thermomechanically treated alloys and after the superplastic deformation. The developed Arrhenius-type mathematical model of superplastic deformation behavior showed excellent predictability for the studied alloys with different solute Mg. • Microstructure and tensile properties for thermomechanical-treated Al–Mg–Er–Zr alloys were studied. • A L1 2 -Al 3 (Er,Zr) precipitates parameters were studied after annealing of as-cast and rolled samples. • Increase in Mg solute improved solid solution strengthening and superplastic properties. • Model with excellent predictability of the superplastic deformation behavior was developed.

Effect of Nano-Si3N4 Reinforcement on the Microstructure and Mechanical Properties of Laser-Powder-Bed-Fusioned AlSi10Mg Composites

Laser powder bed fusion (LPBF) technology is of great significance to the rapid manufacturing of high-performance metal parts. To improve the mechanical behavior of an LPBFed AlSi10Mg alloy, the influence of nano-Si3N4 reinforcement on densification behavior, microstructure, and tensile property of AlSi10Mg was studied. The experimental results show that 97% relative density of the 3 vol.% nano-Si3N4/AlSi10Mg composite was achieved via optimization of the LPBF process. With the increase in the nano-Si3N4 content, the tensile strength and the yield strength of the composite steadily increase as per the Orowan strengthening mechanism while the elongation decreases. In addition, nano-Si3N4 reinforcement reduces the width of the coarse cell structure region and the thermal influence region of the AlSi10Mg matrix. After annealing, the tensile strength of the nano-Si3N4/AlSi10Mg composite decreases and the elongation increases significantly.