Orowan Strengthening Mechanism Research Articles

Synergetic effect of GNPs and MgOs on the mechanical properties of Mg–Sr–Ca alloy

Novel Mg composite was fabricated to explore the synergetic effect of GNPs and MgOs on the microstructure evaluation, deformation behavior and mechanical properties of Mg–Sr–Ca alloy. The addition of hybrid reinforcement into the Mg–Sr–Ca alloy led to considerable grain refinement (~53%). The GNPs were homogeneously dispersed in the matrix alloy where they were randomly distributed revealing the pulling out and pulling off performance. The MgOs were accumulated on the surface of GNPs as a result of the synergetic effect of 1 + 1<2 of hybrid reinforcement by Orowan and thermal mismatch strengthening mechanisms. The yield strength of the hybrid composite at both tensile and compressive tests was improved 19.5% and 38.9% respectively. Significantly synergetic effect of hybrid reinforcement was presented by improvement of failure strain at both tensile and compressive tests (~86.5% and ~20.4%, respectively) due to grain refinement and reduction of eutectic phase (~85%). Conversion of detwinning into the dominant slip mechanism in tensile loading and reduction of twin boundaries motion in compressive loading due to addition of hybrid reinforcement resulted hardening phenomena. Also, the Mg–Sr–Ca/GNP + MgO composite illustrated a low corrosion rate in the SBF solution. Comparative plot indicated that novel composites can be considered for the wide range of applications.

Hot rolling of MWCNTs reinforced Al matrix composites produced via spark plasma sintering

Aluminum/CNT nanocomposite sheets, with appropriate dispersion and interfacial bonding, were fabricated by a combination of powder metallurgy, spark plasma sintering (SPS), and hot rolling. The effects of CNT content as well as plastic deformation, on the microstructure and mechanical properties of the obtained nanocomposite, were investigated. The composite reinforced by 0.5 wt.% CNTs showed an optimal dispersion of CNTs into the aluminum matrix after both SPS and hot rolling. Minimum CNT damage and minimum carbide formation were observed after hot rolling. The best comprehensive mechanical properties corresponded to the sheet of Al-0.5 wt.% CNT nanocomposite thanks to the strong interfacial bonding between Al and CNTs, full densification of the nanocomposites as well as the uniform dispersion of the CNTs into the aluminum matrix. Hardness measurements showed that the maximum hardness was obtained for sheets containing 1.5 wt.% CNTs in both the as-SPS and the as-hot rolled conditions. Load transfer, Orowan, and grain size strengthening mechanisms could affect the increase of strength as well as the combination of strength and ductility of the sheets of Al-CNT nanocomposites.

Effects of temperature field and SiC nanoparticles on microstructure and mechanical properties of n-SiCp/Mg-9 %Al composites fabricated by ultrasonication-assisted semi-solid hot pressing of powder

Abstract Mg-9 %Al magnesium matrix nanocomposites reinforced by 5 wt.% nanometre-sized SiC particles were synthesized via semi-solid powder hot pressing assisted by ultrasonication. The effect of the temperature field on the microstructure and tensile properties of the nanocomposites was systematically investigated. The distribution of the SiC nanoparticles, grain size, and morphology of the Mg17Al12 phase were found to be greatly affected by the hot-pressing temperature, resulting in strength and ductility first increasing and then decreasing with increasing hot-pressing temperatures. As the hot-pressing temperature increased to 510 °C, the nanocomposites consisted of hard SiC nanoparticles and isolated soft phases, and the SiC nanoparticles bonded well with the matrix without interfacial activity and exhibited the most uniform distribution in the nanocomposite. Moreover, compared to the Mg-9 %Al alloy, the nanocomposites exhibited significantly improved strength and excellent ductility both at room temperature and elevated temperature. The enhanced mechanical properties were attributed to the Orowan strengthening mechanism, the obvious grain boundary strengthening, and the load transfer effect.

Effect of Friction Stir Processing on Microstructure and Mechanical Properties of AlSi10Mg Aluminum Alloy Produced by Selective Laser Melting

Friction stir processing (FSP) was successfully applied to AlSi10Mg alloy produced by selective laser melting. The microstructure, microhardness, and room-temperature tensile property of the FSPed AlSi10Mg alloy were investigated. The results showed that FSP eliminated the pores of the AlSi10Mg alloy and achieved the microstructural refinement, homogenization, and densification. The grain size was refined from 13.6 μm to 2.3 μm, and relative density increased from 93.3% to 99.6%. An increase in rotation speed led to the enhancement in the density; however, it slightly affected the grain size in this study. The Si particles were homogenously dispersed in the Al matrix, which resulted in uniform distribution of microhardness. FSP led to the increase in the elongation of the AlSi10Mg alloy by 298%, while ultimate tensile strength decreased by only 8%. The Orowan and dislocation strengthening mechanisms were responsible for the loss of strength. FSP has the advantage of acquiring good ductility while maintaining high strength.

Interplay between Single Phase Solid Solution Strengthening and Multi-Phase Strengthening in the Same High Entropy Alloy

High entropy alloys (HEAs) offer the opportunity to achieve an unprecedented balance of properties by accessing novel multi-scale microstructural combinations. Despite the large range of combinations of strength and ductility reported in HEAs, the complex interplay between multiple strengthening mechanisms has not been addressed. The single-phase fcc solid solution state of the Al0.3CoCrFeNi alloy exhibits a strong Hall-Petch hardening effect with reducing grain size. While the same alloy can be strengthened by a composite reinforcement effect of hard intermetallic B2 and sigma precipitates, within a fine-grained fcc matrix, such precipitation leads to solute depletion within the parent fcc matrix, resulting in a substantially reduced Hall-Petch hardening effect. Additional formation of nanoclusters within the matrix fcc phase can strengthen the same alloy to1.85 GPa at room temperature, via an Orowan strengthening mechanism. This complex interplay between strengthening mechanisms, operative at different length scales, forms the subject of the present paper.

Effects and distribution of TiC on the nanoparticle strengthening A-TIG welded AZ31 magnesium alloy joints

AZ31 magnesium alloy sheets were A-TIG welded using mixed activating flux, which contained different ratio of TiC nanoparticles (TiCp) and TiO2 powder, as surface coating. From mechanical test, the values of ultimate tensile strength and microhardness increased from 120.2 MPa to 181.7 MPa, 46.4 HV to 84.2 HV, respectively, which mainly resulted from the grain boundary strengthening of α-Mg and the dispersion strengthening of TiCp. The theoretical calculation suggested that the improvement of the yield strength was mainly the combination of the Hall-Petch and Orowan strengthening mechanisms, and the mismatch strain caused by different coefficient of thermal expansion between the matrix and the particles. Numerical simulation showed that the TiCp had a centralized tendency toward middle and bottom part of welding pool and was confirmed by the micro-zone microhardness test results in the fusion zoon.

Self-assembly of TaC@Ta core–shell-like nanocomposite film via solid-state dewetting: Toward superior wear and corrosion resistance

The improvement of comprehensive properties including hardness, toughness, wear, and corrosion resistance in the transition-metal carbides/nitrides (TMC(N)) films, especially avoiding the trade-off between the hardness and toughness, is strongly required for various applications. Herein, we provide a new strategy, by activating solid-state dewetting during layered deposition, to accomplish the self-assembly of ordered TaC@Ta core–shell-like nanocomposite film consisting of TaC nanocrystallines encapsulated with thin pseudocrystal Ta tissues (∼1.5 nm). The novel core−shell-like structure can simultaneously achieve superhardness (∼45.1 GPa) mainly dominated by the Orowan strengthening mechanism and high toughness attributed to the indenter-induced phase transformation from the pseudocrystal to body-centered cubic α-Ta, together with drastically enhanced wear and corrosion resistance. Furthermore, thin pseudocrystal Ta encapsulated layer (∼1.5 nm) in the TaC@Ta core–shell-like structure helps for promoting the formation of lubricious TaOx Magnéli phase during sliding, thereby further dropping the coefficient of friction relative to TaC monolayer. Apparently, solid-state dewetting may provide a new route to construct ordered TMC(N)@TM core–shell-like nanocomposite structure capable of combining superhardness, high toughness, low friction, and superior wear and corrosion resistance.

Strengthening effects of encapsulating graphene in SiC particle-reinforced Al-matrix composites

This work aims to reveal the strengthening effects of encapsulating graphene in the tensile strength of SiC particulate Al-based composites. Modified theoretical models are discussed regarding the thermal mismatch, Orowan and fine-grain strengthening mechanisms. It is found that the thermal mismatch strengthening is the dominant mechanism among them, followed by the Orowan strengthening and the fine-grain strengthening to be the last. While comparing the effects of two different types of graphene, we find that sheet graphene makes more strengthening contributions to both thermal mismatch and Orowan strengthening mechanisms compared with encapsulating graphene. Finite element simulations are employed to investigate the variation patterns of these effects with varies particle sizes and volume fractions. A better enhancing effect of encapsulating graphene can be achieved with a larger volume fraction and a smaller particle size.

Microstructure and mechanical properties of an in-situ TiB2/Al-Zn-Mg-Cu-Zr composite fabricated by Melt-SHS process

A 10 vol% TiB2/Al-Zn-Mg-Cu-Zr composite was prepared by Melt-SHS techniques. The microstructures and mechanical properties of the composite were analyzed in this work. The results show that TiB2 particles with an average particle size of 0.67 µm are dispersed in the composite uniformly well combined with the matrix alloy after hot extrusion and T6 treatment. The addition of TiB2 particles resulted in a grain size reduction by 64.4%. The hardness, UTS, TYS and elastic modulus of the composite are increased by 9%, 20.2%, 22.3% and 24.6%, respectively. However, the elongation is reduced with the addition of TiB2 particles. The improvement of yield strength is attributed to the uniform dispersion of the fine TiB2 particles in the alloy matrix and the major contribution is from the dislocation strengthening mechanism, which has an additional contribution of 13.8%. In addition, the Orowan strengthening mechanism, grain refinement and load bearing strengthening mechanism have also contributed.

Effect of Al2O3 Nanoparticles as Reinforcement on the Tensile Behavior of Al-12Si Composites

Al2O3 nanoparticle-reinforced Al-12Si matrix composites were successfully fabricated by hot pressing and subsequent hot extrusion. The influence of weight fraction of Al2O3 particles on the microstructure, mechanical properties, and the corresponding strengthening mechanisms were investigated in detail. The Al2O3 particles are uniformly distributed in the matrix, when 2 and 5 wt. % of Al2O3 particles were added to the Al-12Si matrix. Significant agglomeration can be found in composites with 10 wt. % addition of Al2O3 nanoparticles. The maximum hardness, the yield strength, and tensile strength were obtained for the composite with 5 wt. % Al2O3 addition, which showed an increase of about ~11%, 23%, and 26%, respectively, compared with the Al-12Si matrix. Meanwhile, the elongation increased to about ~30%. The contribution of different mechanisms including Orowan strengthening, thermal mismatch strengthening, and load transfer strengthening were analyzed. It was shown that the thermal mismatch strengthening has a more significant contribution to strengthening these composites than the Orowan and load transfer strengthening mechanisms.

Microstructure and Tensile Properties of n-SiCp/Mg-9%Al Composites Prepared by Ultrasonic Assisted Hot Pressing of Powder

In this paper, the Mg-9%Al alloy reinforced by 5 wt.% SiC nanoparticles was fabricated by hot pressing of powder with ultrasonic vibration under a semi-solid state. The influence of hot-pressing temperature on the microstructure and mechanical properties of the n-SiCp/Mg-9%Al composite was investigated. The results indicated that the density of the composite was increased significantly and the agglomeration of SiC nanoparticles was evidently reduced with the increase in the hot-pressing temperature from 450 to 510 °C. Additionally, the elevated hot-pressing temperature resulted in remarkable grain refinement. However, as the hot-pressing temperature increased to 530 °C, the density decreased and the average grain size increased, which caused a decline in the mechanical properties. The study of the interface between the n-SiCp and the matrix in the nanocomposite suggested that n-SiCp bonded well with the matrix without interfacial activity. The ultimate tensile strength, yield strength and elongation to fracture of the nanocomposites were simultaneously enhanced compared with that of the Mg-9%Al alloy. This improvement could be attributed to obvious grain refinement and the Orowan strengthening mechanism.

The phase transformation and strengthening of a Cu-0.71 wt% Cr alloy

Abstract The phase transformation of a Cu-0.71 wt% Cr alloy during the aging process at 450 °C was investigated by Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) in the study. The strengthening mechanism was studied as well. The precipitation sequence of Cu-0.71 wt% Cr aged at 450 °C is supersaturated solid sloution→G.P zones (fcc Cr-rich phase)→fcc Cr phase→order fcc Cr phase→bcc Cr phase. This transformation can be achieved by the nucleation of coherent fcc spherical precipitates and growth and transformation of fcc precipitates into the bcc structure. When the specimen is aged aging for 1 h–24 h, both fcc and bcc precipitates exist in the matrix simultaneously. Ordering process is found during the aging process, which is in favor of the precipitation of Cr-rich phases. The orientation relationship between bcc Cr precipitates and the matrix exhibit NW-OR. The peak strength effect occurs after aging for about 8 h and the strength continues to decrease with prolonging aging time, indicating overaging. The strengthening effect of Cr-rich phase precipitated in aging at 450 °C for 8 h is calculated to be 146 MPa on the basic of the Orowan strengthening mechanism, which is in quite accordance with the experimental data (144.5 MPa).

A Scandium Modified Al-0.7 Fe Binary Alloy: Improvement of Creep- Resistance Property

The creep behaviors and microstructures of Al-0.7Fe and Al-0.7Fe-0.2Sc alloy are investigated through creep tests, optical microscope, electron probe micro-analyze and transmission electron microscope observations. It is found that the steady state creep rates of Al-0.7Fe-0.2Sc are smaller than that of Al-0.7Fe under different temperatures at 70 Mpa. An overview of microstructure is given, the interactions between intermetallic phases and dislocations are investigated, with an emphasis on the Al3Sc precipitates. The mechanism controlling creep-resistance is explained by Orowan strengthening mechanism. The magnitude of Δσ Or can afford dislocations to bypass Al3Sc precipitates in Al-0.7Fe-0.2Sc alloy. The counter flow of the vacancies and solute atoms are induced to expound the dislocation motion mechanism.

Microstructural Characteristics and Mechanical Properties of Friction Stir Welded Thick 5083 Aluminum Alloy

Joining thick sections of aluminum alloys by friction stir welding (FSW) in a single pass needs to overcome many challenges before it comes to full-scale industrial use. Important parameters controlling the structure-properties relationships both across weld cross-section and through thickness direction were investigated through mechanical testing, electron backscatter diffraction technique, transmission electron microscopy, and occurrence of serrated plastic flow. The evolution of the properties in the weld cross-section shows that the presence of undissolved and fragmented Al $$_6$$ MnFe particles cause discrepancies in establishing the Hall-Petch relationship, and derive the strengthening from the Orowan strengthening mechanism. A ‘stop action’ friction stir weld has been prepared to understand the role of geometrical features of the tool probe in the development of the final microstructure after complete weld. Sectioning through the ‘stop action’ weld with the probe in situ displays the individual effect of thread and flat on the grain structure formation. The material at the thread surface experiences more severe deformation than the material at flat surface. Both the high-angle boundaries and mean grain size are found to be higher at the thread surface. The strain hardening capacity, stress serration amplitude, and frequency are observed to be higher in the stir zone than other weld regions.

Strengthening Mechanisms in Nanostructured Al/SiCp Composite Manufactured by Accumulative Press Bonding

The strengthening mechanisms in nanostructured Al/SiCp composite deformed to high strain by a novel severe plastic deformation process, accumulative press bonding (APB), were investigated. The composite exhibited yield strength of 148 MPa which was 5 and 1.5 times higher than that of raw aluminum (29 MPa) and aluminum-APB (95 MPa) alloys, respectively. A remarkable increase was also observed in the ultimate tensile strength of Al/SiCp-APB composite, 222 MPa, which was 2.5 and 1.2 times greater than the obtained values for raw aluminum (88 MPa) and aluminum-APB (180 MPa) alloys, respectively. Analytical models well described the contribution of various strengthening mechanisms. The contributions of grain boundary, strain hardening, thermal mismatch, Orowan, elastic mismatch, and load-bearing strengthening mechanisms to the overall strength of the Al/SiCp microcomposite were 64.9, 49, 6.8, 2.4, 5.4, and 1.5 MPa, respectively. Whereas Orowan strengthening mechanism was considered as the most dominating strengthening mechanism in Al/SiCp nanocomposites, it was negligible for strengthening the microcomposite. Al/SiCp nanocomposite showed good agreement with quadratic summation model; however, experimental results exhibited good accordance with arithmetic and compounding summation models in the microcomposite. While average grain size of the composite reached 380 nm, it was less than 100 nm in the vicinity of SiC particles as a result of particle-stimulated nucleation mechanism.

Fabrication and properties of ZrO2/AZ31 nanocomposite fillers of gas tungsten arc welding by accumulative roll bonding

In the present study, a new method for fabricating ZrO2/AZ31 nanocomposite fillers of gas tungsten arc (GTA) welding was developed by applying accumulative roll bonding (ARB) to the magnesium sheets coated with ZrO2 nanoparticles. The purpose of ARB was to create a uniform dispersion of ZrO2 nanoparticles in the fillers and to form a good interfacial bonding between the magnesium matrix and ZrO2 nanoparticles. After welding, the effect of ZrO2 nanoparticles on the microstructure and mechanical properties of weld was evaluated. The test results showed that the yield strength of weld was greatly increased when using the nanocomposite fillers. The improvement in the yield strength was attributed to the grain refinement, coefficient of thermal expansion mismatch and Orowan strengthening mechanisms.

Relationships among microstructure, precipitation and mechanical properties in different depths of Ti–Mo low carbon low alloy steel plate

Ti–Mo low carbon low alloy steel plate with 25mm in thickness was produced through hot rolling in laboratory condition. Relationships among microstructure, precipitation and mechanical properties in different depths were investigated and the results revealed that substructures, such as dislocations and low angle boundaries, could vary the process of precipitation and finally made the mechanical properties changed from different depths. Mainly influenced by the high cooling rate during γ–α phase transition process, surface region of the plate was characterized by quasi-polygonal ferrite and large (Ti,Mo)C carbides (>10nm). However, due to the relatively low cooling rate, some polygonal ferrite formed in the 1/2 thickness region, leading to the promotion of cluster precipitation. Different with the large (Ti,Mo)C carbides heterogeneously nucleated in the substructures, small (Ti,Mo)C carbides (∼2nm) embedded in the precipitation cluster could homogeneously nucleate in the matrix and exhibited a coherent or semi-coherent interface. Besides, the fact that Ti/Mo atomic ratio increased with the size of (Ti,Mo)C carbides further confirmed the promoting effect of Mo during the nucleation process. Different with the Orowan strengthening mechanism, the movement of dislocation could traverse precipitation clusters. The formation of TiN during smelting process is harmful to the mechanical properties, thus a better performance can be achieved through the reasonable control of it.

Novel manufacturing process of nanoparticle/Al composite filler metals of tungsten inert gas welding by accumulative roll bonding

In the present work, accumulative roll bonding (ARB) was used as an effective method for manufacturing nanoparticle/Al composite filler metals of tungsten inert gas (TIG) welding. After welding, the distribution of ceramic nanoparticles and mechanical properties of welds were investigated. By applying ARB, ceramic nanoparticles were uniformly dispersed in the composite filler metals. Consequently, the welds produced by these filler metals had a uniform dispersion of ceramic nanoparticles in their compositions. The test results showed that the yield strength of welds was greatly increased when using the nanoparticle/Al composite filler metals. The improvement in the yield strength was attributed to the coefficient of thermal expansion mismatch and Orowan strengthening mechanisms. Therefore, according to the results presented in this paper, it can be concluded that the nanoparticle/Al composite filler metals can serve as a novel filler metal for TIG welding of aluminum and its alloys.

Coble, Orowan Strengthening, and Dislocation Climb Mechanisms in a Nb-Modified Zircaloy Cladding

Biaxial creep tests on HANA-4 tubes, Nb-added Zircaloy-4 were conducted using internal pressurization of closed-end tubes to investigate the rate-controlling mechanisms over a range of hoop stresses, \( 8.38 \times 10^{ - 5} E - 2.87 \times 10^{ - 3} E \), at three different temperatures 673 K, 723 K, and 773 K (400 °C, 450 °C, and 500 °C). The mechanistic creep parameters such as stress exponent (n) and activation energy (Q C) were then determined from steady-state creep rates. Based on the variance in stress exponent with respect to the applied stress, three regimes have been identified: a stress exponent close to 1 at low stresses that increased to 3 at the intermediate stresses, which became 4.5 at high stresses. An activation energy value of 226 kJ/mol was evaluated for the n = 3 and n = 4.5 regimes, which lies close to the activation energy for self-diffusion (Q L) in α-Zr alloys. Further, TEM analyses of crept microstructures and comparison of experimental results with standard models were undertaken to find out the rate-controlling mechanisms. Coble creep, climbing of dislocations to bypass β-Nb precipitates, and dynamic recovery by edge dislocation climb are proposed as the rate-controlling mechanisms in the n = 1, n = 3, and n = 4.5 regimes of HANA-4, respectively.

Homogeneous and ultrafine-grained metal matrix nanocomposite achieved by accumulative press bonding as a novel severe plastic deformation process

Accumulative press bonding (APB) is proposed as a novel method for inducing severe plastic deformation. This process can produce a homogeneous and ultrafine-grained nanocomposite, which is extremely difficult to obtain by other processes. AA1050/SiCp nanocomposite with an average grain size of 280 nm and well-developed high-angle grain boundaries (39° average misorientation angle and 82% high-angle boundaries) exhibited the highest tensile strength reported in the literature, i.e. 284 MPa. Theoretical models revealed that the contributions of Orowan and grain refinement strengthening mechanisms to yield strength were 76.6% and 14.8%, respectively.