Orowan Strengthening Research Articles

Achieving an unprecedented strength-ductility balance of molybdenum alloy by homogeneously distributing yttrium-cerium oxide

Rare earth (Y/Ce) were homogeneously distributed in molybdenum alloys by liquid-liquid doping and powder metallurgy method, and the molybdenum alloys plates were obtained after rolling. The results show the rare earth form nanoscale Y2O3 and CeO2 particles which were concomitant in molybdenum matrix. The rare earth oxides particles significantly refine microstructure and improve mechanical properties of the rolled molybdenum plate. The adding of 0.8%Y2O3 and 0.12%CeO2 made the micro fringe spacing in microstructure of rolled molybdenum alloy reduce 52.43%. The newly developed molybdenum alloys have an unprecedented strength-ductility balance compared with previous other molybdenum alloys. And high tensile strength and elongation were obtained simultaneously. The tensile strength of the rolled Mo-0.8%Y2O3-0.12%CeO2 alloy plate reaches 917 MPa with a 13.9% elongation, increased by 21.9% and 55.5% over a pure molybdenum plate, respectively. The strength-elongation product of the new molybdenum alloy annealed at 1200 ℃ could reach 2.4 times that of pure molybdenum. The addition of the nanoscale rare earth oxides to the Mo-alloy introduces Orowan strengthening and fine grain strengthening which changes fracture mode, resulting in excellent strength-ductility balance.

Grain refinement and strengthening of 316L stainless steel through addition of TiC nanoparticles and selective laser melting

In this work, strengthening of 316L stainless steel was achieved through addition of 1 and 3 wt% TiC nanoparticles. The TiC nanoparticles and 316L powders were mixed using low energy ball milling and then processed by selective laser melting. The grains are significantly refined from 16.8 μm to 6.9 μm with the addition of 3 wt% TiC nanoparticles. Addition of 1 and 3 wt% TiC nanoparticles remarkably increased yield strength (694 MPa and 773 MPa) and ultimate tensile strength (888 MPa and 988 MPa). Meanwhile, the tensile elongation was kept at a high level (47% and 32%). The strength enhancement primarily results from Orowan strengthening by the nanoparticles, and the reduction of ductility is related to the suppression of twinning induced plasticity.

High-strength Al matrix composites reinforced with uniformly dispersed nanodiamonds

Poor dispersion of nanodiamonds (NDs) is the bottleneck to exploit their intrinsically excellent properties in metal matrix composites (MMCs). In this study, a strategy of surface modification was developed to uniformly disperse ND particles into 2024 aluminum alloy. Microstructure observations showed that individual NDs are closely contacted with the matrix, forming reaction-free interfaces. Consequently, a high-strength 0.8 vol% ND/2024Al composite with an ultimate tensile strength of 741.0 MPa is developed. Theoretical and experimental measurements prove that the strength improvement of ND/2024Al composite is mainly attributed to the Orowan strengthening, thermal mismatch strengthening and grain refinement strengthening. This work demonstrates the effective application of NDs as a reinforcement for MMCs towards high-specific-strength materials.

Semicoherent strengthens graphene/zinc scaffolds

Reduced graphene oxide (RGO) shows great advantages as nano reinforcement for zinc (Zn)-based implants owing to its excellent fracture strength, large specific surface area, and good biocompatibility. Nevertheless, the poor interfacial bonding between Zn matrix and RGO impairs the strengthening efficiency. In this work, titanium carbide (TiC) was used as an interface bridging between Zn matrix and RGO to improve the interface adhesion. On the one hand, TiC was in-situ generated on RGO plane through chemical vapor deposition and tightly integrated together via chemical bond. On the other hand, a semicoherent bonding was formed between TiC and Zn matrix because of the small lattice misfit and similar atomic arrangement between the (200)Zn plane and (002)TiC plane. The results showed that TiC@RGO offered an improved strengthening efficiency with tensile strength of scaffolds increasing from 30.6 to 59.9 MPa, as the TiC nanoparticles considerably enhanced the load transfer strengthening of RGO and contributed an Orowan strengthening. Significantly, it also improved the plasticity of Zn scaffolds because the semicoherent structure inhibited the premature stress concentration and dislocation accumulation. Moreover, TiC@RGO promoted the cell differentiation behavior of Zn scaffolds.

Wire arc additive manufacturing of AA5183 with TiC nanoparticles

Aluminium alloys processed by wire arc additive manufacturing (WAAM) exhibit a relatively coarse microstructure with a columnar morphology. A powerful measure to refine the microstructure and to enhance mechanical properties is to promote grain refinement during solidification. Addition of ceramic nanoparticles has shown great potential as grain refiner and strengthening phase in aluminium alloys. Thus, an Al-Mg alloy mixed with TiC nanoparticles was manufactured by the novel metal screw extrusion method to a wire and subsequently deposited by WAAM. Measures to restrict oxidation of magnesium during metal screw extrusion were examined. Purging of CO2 gas into the extrusion chamber resulted in a remarkable reduction in formation of MgO and Mg(OH)2. TiC decomposed to Al3Ti during WAAM deposition, leading to a significant grain refinement of 93% compared to a commercial benchmark. The presence of remaining TiC nanoparticles accounted for an increased hardness of the WAAM material through thermal expansion mismatch strengthening and Orowan strengthening. Exposure of TiC to moisture in air during metal screw extrusion increased the internal hydrogen content significantly, and a highly porous structure was seen after WAAM deposition.

The effects of in-situ ZrB2 particles and Gd on the solidification behavior and mechanical properties of AA6111 matrix composites

In this research work, the new AA6111 matrix composites reinforced by the cooperation of nano ZrB2 particles and Gd had been designed and fabricated via in situ reaction. The addition of Gd made the nano ZrB2 particles uniformly dispersed due to the reduction of solid-particle interfacial energy (σsp) by keeping the low-energy orientation relationship. Meanwhile, it promotes the formation of equiaxed grains whose formation is also based on the nano-sized reinforcing phases as the hindering of dendrite coherency points are related to the growth restriction factor (GRF) and as the pinning effect to the grain boundaries. The fluidity was improved because of uniform viscosity and dendrites avoided meeting with the neighboring ones by the entrapment of nano-sized reinforcing phases like AlGd and ZrB2. The results indicated that AA6111–0.5 wt. % Gd-2 vol. % ZrB2 composites possessed the longest fluidity length of 70 mm. Meanwhile, the composites displayed increases of 32.7 %, 47.3 % and 52.8 % in YS, UTS and elongation, respectively, compared to the matrix alloy. A notable lattice distortion of the matrix near the ZrB2 particles and AlGd phases was proclaimed via Geometric Phase Analysis (GPA) analysis. Strengthening mechanism comprehending yield strength, containing Orowan strengthening, grain refinement strengthening, was integrally elaborated.

Exploiting the rapid solidification potential of laser powder bed fusion in high strength and crack-free Al-Cu-Mg-Mn-Zr alloys

This work describes a systematic alloy design strategy resulting in the development of a high strength aluminum alloy adopted for L-PBF. First, based on the composition of a reference Al-Cu-Mg alloy, three Al-Cu-Mg-Mn-Zr-based alloys were investigated using computational thermodynamic tools. Subsequently, the L-PBF processing behavior, microstructure, and concomitant mechanical properties of the L-PBF-fabricated alloys were investigated. Alloys with different compositions showed substantial differences in microstructure: the alloy without Zr addition showed a coarse columnar microstructure and suffered from solidification cracking, alloys with low to mediate Zr additions (1–1.98 wt%) showed a mixed columnar and equiaxed microstructure, while alloys with high Zr addition (3.72 wt%) showed a fully equiaxed microstructure, accompanied by a grain size reduction down to 0.7 ± 0.3 µm. All alloys containing ≥ 1.98 wt% Zr were crack-free. The L-PBF-processed Al-4.40Cu-1.51Mg-1.15Mn-3.72Zr (wt%) alloy showed an extended Zr solid solubility in the Al matrix of ~ 1.3 ± 0.1 wt%. Coherent primary Al3Zr particles with a cubic L12 structure were formed in all the Zr-containing alloys. The mechanical properties of as-built alloys increased consistently with increasing Zr contents from 0 to 3.72 wt%. The designed Al-4.40Cu-1.51Mg-1.15Mn-3.72Zr (wt%) alloy combined a yield strength of 561 ± 24 MPa, an ultimate tensile strength of 580 ± 16 MPa, and an elongation at break of 6.0 ± 1.3%. The exceptionally high strength of this alloy is attributed to a combination of grain refinement, Orowan, solid solution, and dislocation strengthening. The current work shows the intrinsic potential of rapid solidification occurring during L-PBF for the fabrication of geometrically-complex, high-strength lightweight parts made of ultra-fine-grained hyper-peritectic aluminum alloys containing transition element additions.

In-situ formation of TiC nanoparticles in selective laser melting of 316L with addition of micronsized TiC particles

316L stainless steel has a wide range of engineering applications. However, its relatively low yield strength limits its applications. In this work, strengthened 316L stainless steel was fabricated via selective laser melting (SLM) with the addition of 3 wt% micronsized TiC particles. The grains of 316L are significantly refined to approximately 3 μm. Although micronsized TiC particles were used as reinforcement, in-situ formed nanosized TiC particles were observed. Tensile tests were carried out and the yield strength of SLM 316L-3TiC was 803 MPa–832 MPa with the elongation ranging from 25.8% to 28.5% when fabricated with laser power between 225 W and 275 W. Relative to SLM 316L without TiC particles which has a yield strength of 599 MPa, the strength enhancement is found to be 97 MPa from grain refinement and 140 MPa from Orowan strengthening.

Influence of V additions on microstructures, tensile and fatigue properties of Al–Zn–Mg alloys

V addition with range from 0–0.09 wt% are added in extruded Al–Zn–Mg alloys to study the influence of V addition induced microstructures on the tensile strength and fatigue properties of Al–Zn–Mg alloys under T74 temper. The V addition significantly inhibits the recrystallization behavior of the alloy via forming Al23V4 second phase particles, and the formation of coarse grain layer on the profile surface is gradually inhibited. The aging hardening curve, tensile strength, and fatigue strength of Al–Zn–Mg alloy with different V content are studied. It is discovered that an increase of V content obviously improves the tensile properties and the median fatigue strength of the investigated alloy, but has little effect on the aging hardening rate of the investigated alloys. In fact, the alloy with 0.09 wt% V content has the highest tensile properties, and its tensile strength and yield strength are 374.4 and 329.0 MPa, respectively. The alloy with 0.05 wt% V content achieves the maximum median fatigue strength, which is 183.6 MPa. After T74 aging treatment, the main strengthening mechanism is Orowan bypass strengthening mechanism. However, the excessive V addition has limited effect on the strength improvement of the studied alloys, and has adverse effects on tensile toughness and fatigue strength, mainly because the V atoms will agglomerate in the aluminum matrix and form micron-sized coarse V-rich particles, with an average particle size of about 10 μm.

Synergistic strengthening effect of tungsten carbide (WC) particles and silicon carbide whiskers (SiCw) on mechanical properties of Cu–Al2O3 composite

Cu–Al2O3 composites are widely used in electrical contact fields because of their excellent electrical conductivity, thermal conductivity and arc erosion resistance. (WC + SiCw)/Cu–Al2O3 composites with better properties were prepared by powder metallurgy combined with an internal oxidation process that introduced micron-sized WC particles and SiCw into the Cu–Al2O3 composite. The synergistic strengthening mechanism effect of nano-Al2O3 particles, micron-sized WC particles and SiCw in copper matrix composites was analyzed. The results show that there is a semi-coherent interface between the nano-Al2O3 particles and the copper matrix. The ultimate tensile strength of the (1WC + 2SiCw)/Cu–Al2O3 composite is 531.6 MPa, which is 12.7% and 4.5% higher than that of the Cu–Al2O3 composite and the SiCw/Cu–Al2O3 composite, respectively. According to theoretical calculations and an analysis of the strengthening mechanism, the contributions of the Orowan strengthening and load transfer strengthening mechanism in the (1WC + 2SiCw)/Cu–Al2O3 composite are 27.3% and 16.6% respectively. The synergistic strengthening effect of particles and whiskers contributed 6.0% to the tensile strength of the (1WC + 2SiCw)/Cu–Al2O3 composite.

Microstructure Refinement and Strengthening–Toughening Mechanisms of Gray Cast Irons Reinforced by In Situ Nanosized TiB2–TiC/Al Master Alloy

Herein, the effects of addition of TiB2–TiC nanoparticles on the microstructure and tensile properties of as‐cast gray cast irons are investigated. The in situ nanosized TiB2–TiC/Al master alloy is added in the casting process. It is found that the presence of TiB2–TiC nanoparticles refines the graphite flakes and pearlite and increases the yield strength, tensile strength, and fracture strain simultaneously. The strengthening mechanisms are related to grain refining strengthening and Orowan strengthening. The toughening mechanism is related to the scattering behavior of cracks by nanoparticles.

Zr-containing precipitate evolution and its effect on the mechanical properties of Cu–Cr–Zr alloys

The present work investigates the Zr-containing precipitate evolution and its effect on the mechanical properties of a Cu–Cr–Zr alloy after solution treatment at 1253 K for 2 h and aging at 763 K for 0–6 h. The results show that the precipitation sequence of the Zr-containing precipitates in the Cu–Cr–Zr alloy is supersaturated solid solution→Zr-rich atomic clusters→Cu5Zr phase. Zr atoms first segregate at the {111} crystal plane of the copper and form coherent Zr-rich atomic clusters during the aging process, which are composed of Zr-rich atoms monolayers and exhibit plate-shaped. Some of the Zr-rich atomic clusters is transformed into the more stable phase of Cu5Zr phase as the aging time increases, the habit plane of which is the {111}Cu crystal plane. The contribution of Zr-rich atomic clusters and Cu5Zr precipitates to the yield strength of the alloy is calculated by coherency strengthening and Orowan strengthening, respectively. The total yield strength is very close to the experimentally measured strength.

In situ synthesized nano-Al4C3 reinforced aluminum matrix composites via friction stir processing

The strength-ductility trade-off problem of carbon nanotube (CNT) reinforced aluminum matrix nanocomposites (AMNCs) restricts its further application. Hence, we report the fabrication of nano-Al 4 C 3 reinforced AMNCs through friction stir processing (FSP) on CNT/Al composites which can simultaneously elevate the ductility of the composite and maintain the original strength. The microstructure evolution and the dispersion of reinforcement are investigated. Tensile tests show that the elongation of the Al 4 C 3 /Al composites fabricated via FSP at a rotation rate of 800 rpm increased by 1.6 times than that of CNT/Al composite and the yield strength retained 95%. The improvement of the mechanical properties is due to the strong Al 4 C 3 –Al interface, homogeneous dispersion, nano size, and dynamic recrystallization during FSP. Grain refinement and Orowan strengthening are the main strengthening mechanisms of Al 4 C 3 /Al composites. This research shares an approach to preparing a nano-Al 4 C 3 reinforced aluminum matrix composite with well strength and outstanding ductility.

Effects of Sc and Zr Addition on Microstructure and Mechanical Properties of AA5182.

The effects of 0.1 wt.% Sc and 0.1 wt.% Zr addition in AA5182 on microstructure and mechanical properties were investigated. Results show that Al3(ScxZr1−x) dispersoids formed in AA5182. Observation of ingots microstructures showed that the grain size of 5182-Sc-Zr alloy was 56% lower than that of based AA5182. Isothermal annealing between 230 °C and 500 °C for 2 h was performed to study the recrystallization, tensile properties and dispersoid coarsening. The recrystallization was inhibited by the dispersoids, and the alloy microstructure remained deformed after annealing. Al3(ScxZr1−x) in AA5182 was stable when annealing below 400 °C, while parts of dispersoids coarsened significantly when heating at 500 °C. The addition of Sc and Zr allowed YS of 5182 alloy to achieve 247.8 MPa, which is 100 MPa higher than the corresponding AA5182. The contributions of Orowan strengthening and grain boundary strengthening were obtained by calculation.

An additively manufactured and direct-aged AlSi3.5Mg2.5 alloy with superior strength and ductility: micromechanical mechanisms

An AlSi3.5Mg2.5 (wt%) alloy with excellent mechanical properties was produced via laser powder bed fusion in this study. The yield strength, tensile strength, and elongation of this as-built AlSi3.5Mg2.5 alloy reach about 406 MPa, 501 MPa, and 8.6%, respectively. These properties are dramatically superior to the current additively manufactured Al-Si-Mg alloys. A direct-aging treatment at 170°C for one hour increases the yield strength and ductility further to about 417 MPa and 11.0%, respectively, with the tensile strength remaining the same level. The microstructures and strengthening mechanisms of the as-built and direct-aged samples were investigated systematically. The underlying micromechanical mechanisms of the as-built and direct-aged samples were examined based on a combination of in-situ synchrotron X-ray diffraction and three-dimensional crystal plasticity modeling. The as-built AlSi3.5Mg2.5 alloy possesses a fine microstructure, including fine grains and nano-sized Mg2Si and Si precipitates. After direct-aging treatment, additional Mg2Si and Si precipitate out. Besides, element diffusion upon aging treatment causes migration of cell boundaries and relaxation of residual stress. The direct-aging treatment leads to an increased Orowan strengthening, dislocation strengthening, and load-bearing strengthening effects. Moreover, the variations of microstructure and residual stress after the aging treatment change the dislocation behavior and increase the dislocation storage capacity, causing an increased ductility. Nevertheless, the aging treatment does not alert the type of damage and fracture. This study provides valuable insights to tailor the microstructure and mechanical properties of additively manufactured Al-Si-Mg alloys.

Tribological behaviour of AA7168 hybrid composite sheets for aerospace structures fabricated through COMPO casting

ABSTRACT In this research work, an attempt was made to reinforce AA7168 aluminium alloy with Boron Carbide (B4C) and Silicon Carbide (SiC) through compos casting technique. Tribological test were performed by varying weight percentage (3, 6, 9, 12%), Load (10, 20, 30, 40 N), Sliding velocity (10, 20, 30, 40 m/s) and sliding distance (1000, 2000, 3000, 4000 m). The results revealed that the wear resistance increases with addition of reinforcing particles until a saddle point of 9 wt.% owing to the formation of mechanical mixed layer. At 12%, the wear resistance reduces because of the clustering of particles. Because of the hardness of the particles, the coefficient of friction increases with increasing weight percentage. From Taguchi approach, it was revealed that percentage reinforcement was most influential factor followed by load, sliding velocity and sliding distance. The addition of particles increases the hardness and tensile strength due to the hall petch effect and orowan strengthening. WASPAS technique was utilised to optimise the input variables.

A novel copper-matrix composite with fullerene soot nanoparticles produced by molecular level mixing

The presented work demonstrates the capability of applying fullerene soot nanoparticles as a phase for strengthening of Cu. Copper-fullerene soot composites with 0–5 wt% carbon additions were fabricated by molecular level mixing and hot pressing procedure. The structure was observed by light microscopy, SEM, EBSD, and analyzed by XRD. The hardness, thermal conductivity, and coefficient of friction were investigated. The hardness of the composite continuously increases with carbon soot additions and reaches 128 HB at 5% of fullerene soot. Full strengthening of the composites is mainly attributed to the Orowan strengthening and the grain-size refinement.

Characterization and strengthening effects of different precipitates in Al–7Si–Mg alloy

The microstructure of the nanoscale precipitates (especially the β phase) formed in the primary a-Al grains of a cast Al–7Si–Mg alloy during ageing at different temperatures, and the strengthening effects of them on the mechanical properties have been systematically investigated by transmission electron microscopy (TEM) and tensile test. The interactions of dislocations with different types of precipitates were analyzed in depth. It was found that the GP zones and β″ phase can be easily sheared by dislocations along the close-packed {111}Al planes, leading to good deformation compatibility and elongation. The step-like planar defects were found in the deformed β″ phase, indicating that this needle-shaped precipitate can be sheared not only along the short axis but also along the long axis. The β phase and nanoscale Si particles are usually bypassed by dislocations, showing a typical Orowan strengthening mechanism, leading to the highest strength. This may be related to their large size (about 100 nm in diameter), high shear modulus and modest number density. In addition, the moiré fringes and FFT pattern of β phase were discussed by calculation of diffraction vectors. The moiré fringes with about 2.389 nm and 2.664 nm spacing displayed in HRTEM image results from the interactions between the 004Al/006β and 2¯22Al/3¯33β diffraction respectively. The corresponding complex FFT pattern is caused by strong double diffraction of [110]β and [110]Al reflections. Furthermore, an interesting phenomenon that the β phase tends to nucleate and grow on the surface of Si particle was firstly observed and discussed in depth.

High strength and high ductility nano-Ni-Al2O3/A356 composites fabricated with nickel-plating and equal channel angle semi-solid extrusion (ECASE)

Abstract The nano-Ni-Al2O3/A356 nanocomposites prepared with nickel-plating, stir casting, and equal channel angle semi-solid extrusion (ECASE). The microstructure, tensile property, and fracture morphology of the fabricated nanocomposites have been investigated. The microstructure observation showed the nickel-plating could stimulate nucleation and break nanoparticle aggregation, resulting the matrix grains in a smaller size (63 μm) and the nanoparticles more uniform located on the grain boundary. The ECASE could further refine the grains size (23 μm) and improve the nanoparticle dispersion. Although 5 passes refine the grains to 16 μm, it would cause the particles to re-agglomerate, due to the nanoparticles exist in the semi-solid liquid phase for a long time. The fabricated nanocomposites exhibited an enhancement in both strength and ductility, about 1.2–2.5 times higher than those of the corresponding aluminum matrix composites. Due to the Orowan strengthening and fine grain strengthening, i.e., increased the number of grain boundaries and improved the resistance of particles to cooperative grain deformation. Meanwhile, the ECASE eliminated the intergranular defects and improved the grain boundary bonding. The enhanced mechanical properties of the nanocomposites were attributed to the grain boundary control increased by the nickel-plating and ECASE. The grain boundary control, such as increasing the grain boundary number, improving the particle-matrix adhesion and particle dispersion, can be applied to the development of high mechanical properties aluminum matrix composites.

Ultrahigh strength TiCnp/Mg–2Zn-0.8Sr-0.2Ca magnesium matrix composite processed by combining multidirectional forging with extrusion

A TiCnp/Mg–2Zn-0.8Sr-0.2Ca magnesium matrix composite was processed by the combination of multidirectional forging (MDF) with extrusion (EX). The composite exhibited ultrahigh mechanical properties (yield strength of ~500 MPa and ultimate tensile strength of ~544 MPa) after 6 passes of MDF at 300 °C, followed by EX at 0.1 mm/s and 200 °C. The grain boundary strengthening effect caused by grain refinement and high recrystallization rate, dislocation strengthening effect originated from the severe plastic deformation, as well as the Orowan strengthening effect inspired by the dynamically precipitated MgZn2 phases and the added TiCnp were considered as the main contributors to the substantial increase in strength.