Main Strengthening Research Articles

Effect of aging on the strength of corrosion-resistant incoloy alloys 945 and 945X: A microstructural perspective

The results of this study show that Incoloy 945X is 19.36% harder and 10.91% stronger than Incoloy 945. Of particular interest is the morphology of precipitates responsible for precipitation hardening in both alloys. To identify and understand the physical mechanisms that lead to these results, this study undertook an extensive microstructural study in which γ’ size, shape and elemental constitution was investigated and correlated to the aging conditions. The main strengthening phase for both alloys is identified by transmission electron microscopy to be the main population of γ’ precipitates, which are between 10 and 25 nm in size. Scanning transmission electron microscopy line scans across the γ' precipitate reveal more Nb and Ti deflection in Incoloy 945X than in Incoloy 945. This is further supported by the results of transmission electron microscopy, in which γ’ in 945X appear bright (because of Nb) with faceted growth, resulting in a higher value of 0.2% yield strength (1100 MPa) and hardness (430 HV5) than Incoloy 945.

Investigation of MWCNTs addition on mechanical properties of cordierite glass-ceramic composites

Abstract Cordierite-based glass/ceramic composites reinforced with different volume fractions of carbon nano-tubes were successfully prepared by isostatic pressing. Results showed the increase of flexural strength and fracture toughness of cordierite-based glass/carbon nano-tube composites with carbon nano-tube content. By incorporation of 5 vol.% carbon nano-tubes, the flexural strength and fracture toughness of the composites were increased by up to 50% and 72% compared to the unreinforced cordierite-based glass matrix, respectively. Scanning electron microscopy images indicated that the main strengthening and toughening mechanisms are load transfer, fiber pull out and crack bridging.

The effect of heat treatment on characteristics of the gamma prime phase and hardness of the nickel-based superalloy Rene®80

Abstract In this study, the effect of heat treatment on characteristics of the γ'-Ni3(Al, Ti) phase, as the main strengthening precipitates of the nickel-based superalloy Rene®80 was evaluated in terms of morphology and distribution of the γ' phase, γ (matrix)-γ′(strengthening precipitates) lattice mismatch, and hardness of the alloy. For this purpose, at first, the solution heat treatment was performed at 1204 °C on the alloy. Then, heat treatment cycles were carried out at three temperatures, namely 871 °C, 1095 °C, and 1130 °C, for different periods of time. The microstructures were analyzed by optical microscope and scanning electron microscope. Also, X-ray diffraction analysis was conducted to determine variations of the γ-γ′ lattice mismatch, followed by hardness measurement test, which was performed after each stage of heat treatments. The results showed an increase in the amount and size of the γ' phase with holding time at 871 °C, while the values were seen to remain constant and even decrease at 1095 °C and 1130 °C, respectively, due to simultaneous dissolution of the γ' phase during extended periods of time. At all of the three temperatures, the γ-γ′ lattice mismatch increased with time and showed larger negative values, while an increase in temperature from 871 °C to 1130 °C led to lower γ-γ′ lattice mismatch. The largest lattice mismatch (−0.653%) was observed at 871 °C after a heat treatment time of 1000 s. Hardness of the Rene®80 alloy at 871 °C increased with time, while different behaviors were observed at 1095 °C and 1130 °C, where the hardness decreased for extended heat treatment times. The most significant cause of such changes in hardness might be the coherency elastic strain between the γ and γ' phases, which is affected by the characteristics of the γ' phase and its lattice mismatch with the γ phase.

In Situ Observation of High-Temperature Microstructure Evolution and Phase Transformation of 2195 Al-Li Alloy

By using the high-temperature metallography in situ observation system (HTM IOS), the high-temperature microstructure evolution and phase transformation are investigated as well as the surface oxidation dynamics of 2195 Al-Li alloy in T8 temper. The results indicate that the main strengthening phase of the T8 raw material is T1 (Al2CuLi) phase, which gradually dissolves into the matrix at 300 °C to 400 °C, causing a drastic drop in micro-hardness. The TB phase is distributed on the grain boundaries (GBs), resulting from Cu enrichment in the thin liquid film trapped between solidified α phases. The polygonal τ2(Al7Cu2Fe) phase, on the other hand, cannot be eliminated in the heating process even if the liquidus temperature is reached. In the continuous heating scenario, the GBs start to show themselves at 300 °C to 400 °C, then coarsens and become more obvious at 400 °C to 500 °C, accompanied by the color change of the surface, which is mainly due to the surface oxidation; at last, pond-like melt appear at the triangle area among the grains, or the spots where inclusions are present when the temperature reaches 500 °C to 600 °C. Finally, the oxidation level of the 2195 Al-Li alloy’s surface is found to be dependent on the holding temperature and holding time based on the Arrhenius formula.

Sustainability analysis of transformable low-rise buildings production and construction integration zones

One of the main issues of organizational and technological solutions progress of transformable low-rise buildings with sandwich panels walls (TLB) rapid construction is the improvement of industrial production methods based on the using of high-performance mechanization tools. The working capital efficiency improving makes pre-fabricated transformable buildings the most attractive technical solution for investor and allows you to quickly recoup investments. The traditional measures of the organization processes improvement and specific development directions of the TLB construction production organization in modern conditions are given. The technological component of sustainability has been highlighted. The specifics of its provision in the modern conditions of technical development and increasing innovation have been disclosed. The article defines the prerequisites for main components strengthening of the integration zones elements sustainability in the process of transformable low-rise buildings erection. The tendencies of sustainability concept expanding at different levels of the TLB construction production management are substantiated. Evaluation of its effectiveness determines the relevance of the study. The aim of the work is the development of scientific and methodological foundations for the formation of a regional strategy for prefabricated low-rise construction.

Structure and phase composition of a Ni-based alloy formed by additive manufacturing

A heat-resistant Ni-based alloy was formed by the heterophase laser powder metallurgy. The laser power was the main process parameter and was varied in the 250-750 W range. It was found that the microstructure of the alloy in the longitudinal section of the sample depended on the applied laser power. The structural analysis of the as-deposited materials revealed the presence of Ni3Al as the main strengthening phase along with carbide precipitates.

Corrosion and Anodizing Behavior of T1 (Al2CuLi) Precipitates in Al-Cu-Li Alloy

T1 (Al2CuLi) phase precipitates, the main strengthening precipitates in third generation aluminum-copper-lithium (Al-Cu-Li) alloys, play a critical role in determining the corrosion behavior of these alloys. Herein, the T1 precipitates, sufficiently large to be visualized by scanning electron microscopy, were intentionally grown in a commercial Al-Cu-Li alloy through a high temperature annealing process. The corrosion and anodizing behavior of the alloy associated with individual T1 precipitate plates was subsequently investigated. It was observed that corrosion initiated instantaneously on T1 precipitate plates when the alloy was exposed to laboratory air. When immersed in NaCl solution, T1 precipitate plates corroded through a dealloying process and then, drove anodic dissolution of the adjacent aluminum alloy matrix by forming copper-rich nanoparticles at the sites of dealloyed T1 precipitates. The T1 phase precipitates were anodized relatively faster than the aluminum matrix in tartaric-sulfuric acid solution under a constant voltage of 14 V. The anodic film formed from T1 precipitates was dissolved quickly by the anodizing electrolyte during anodizing at relatively higher temperatures, resulting in cavities of sizes similar to those of T1 precipitate plates.

Selective Laser Melting of Gas Atomized Al–3.02Mg–0.2Sc–0.1Zr Alloy Powder: Microstructure and Mechanical Properties

Additive manufactured Sc modified Al alloys for lightweight application is now arousing widespread attraction. The selective laser melting (SLM) of gas atomized Al–3.02Mg–0.2Sc–0.1Zr powder is studied, with the emphasis on its densification, microstructure, and properties. The intrigued finding is that the very high elongation‐to‐failure of 32.5% is obtained with medium tensile strength of 373 MPa after heat treatment of SLM sample. The average relative density is about 98.3% at a volumetric energy density range of (VED) 42–111 J mm−3. The microstructure of produced sample shows cracks but it can be inhibited by increasing the VED. At an excessive VED, the weld pool is transformed from heat conduction to keyhole mode owing to the metal evaporation. Nano‐sized Al3(Sc,Zr) precipitates with a diameter of 5–50 nm are observed, which is responsible for the main strengthening mechanism. The underlying mechanisms of metallurgical defects, weld pool mode and mechanical properties are also illuminated.

On the microstructure, mechanical properties and wear resistance of an additively manufactured Ti64/metallic glass composite

Selective laser melting (SLM) provides flexibility in creating novel metal-matrix composites (MMCs) with unique microstructures and enhanced mechanical properties over conventionally manufactured MMGs. In this study, a Zr-based metallic glass (MG) decorated Ti6Al4V (Ti64) composite with a unique hybrid nanostructure and enhanced mechanical properties and wear resistance was fabricated using SLM. The results revealed that a near-full dense and crack-free Ti-based composite was produced, with its reinforcements consisting of ultrafine β dendrites set with partially crystallized MG nanobands uniformly distributed along the boundaries of the melt pool. The addition of MG significantly affected the solidification behavior of the Ti-liquid because of its higher dynamic viscosity and density as well as compositional effect on the phase stability. With such a unique nanostructured reinforcement, the Ti64/MG composite exhibited an enhanced yield strength (>1 GPa) with reasonable ductility and fracture toughness. On the basis of the result of a theoretical analysis, we attributed the main strengthening mechanism to Orowan strengthening. The wear resistance was also much improved in the Ti64/MG composite, arising from the higher hardness of the nanostructured reinforcement and the formation of a more protective tribo-oxide layer during sliding. The confinement of the 3D distributed reinforcement phase played a crucial role in preventing the delamination of the tribo-layer on the matrix. This work opens a pathway to the design of novel additively manufactured MMCs with outstanding mechanical properties.

The structure and properties of Inconel 718 superalloy powder prepared by vacuum induction melting gas atomization for laser direct metal deposition

Inconel 718 superalloy powder is one of the main materials for laser direct metal deposition aero parts, and the characteristics of alloy powder have an important impact on the microstructure and properties of the formed parts. In this paper, Inconel 718 superalloy powder for laser direct metal deposition was prepared by vacuum induction melting gas atomization. The results show that the degree of sphericity of the prepared alloy powder is 98% and the particle size distributed within the scope of 1–150 μm. The flowability is 15.2 s/50 g, the apparent density is 4.93 g cm−3, the rate of hollow sphere is 4%, the matrix phase of the alloy powder is γ phase and the strengthening phase consists of the main strengthening phase γ′, the auxiliary strengthening phase γ′ and a small amount of carbide MC. After laser forming, the microstructure is dense with few defects, the phase composition is consistent with the powder phase composition. The tensile strength of laser direct metal deposited samples is 822.3 MPa. The elongation is 12.8%, and the hardness is about 275 HV0.2. The Inconel 718 superalloy powder prepared by VIGA has good powder characteristics and meets the requirements of alloy powder characteristics required for laser direct metal deposition.

Effect of particle size ratio on microstructure and mechanical properties of aluminum matrix composites reinforced with Zr48Cu36Ag8Al8 metallic glass particles

Aluminum matrix composites reinforced with Zr48Cu36Ag8Al8 glassy particles were synthesized by powder metallurgy using reinforcement particles larger than the matrix. The effect of the matrix to reinforcement particle size ratio (PSR) on the microstructure and mechanical properties was studied. The results show that high densification (relative density > 98%) was achieved and the glassy particles retained the amorphous structure in all the composites. Quantitative particle distribution analysis in the three-dimensional space indicated that the homogeneity distribution index decreases with reducing PSR. The findings suggest that a ratio of 1/3 ≤ PSR ≤ 1 can be used to obtain composites with rather homogenous distribution of the reinforcement particles. Both compressive and tensile yield strengths of the composites are not sensitive to the PSR change (in the range of 1/3–1/6), whereas the ultimate tensile strength and the ductility are significantly reduced with decreasing PSR; this behavior is accompanied by the change of the fracture mode. The experimental yield strength was found to be consistent with the quantitative strengthening mechanism calculations, and indicated that the reduced matrix ligament size, the thermal mismatch and load bearing are the main strengthening contributions.

Impeding effect of the Al3(Er,Zr,Li) particles on planar slip and intergranular fracture mechanism of Al-3Li-1Cu-0.1Zr-X alloys

The microstructure and mechanical properties of Al-3Li-1Cu-0.1Zr-xEr (x = 0, 0.1) alloys were investigated. With an addition of 0.1 wt% Er, dispersive core-shell structure Al3(Er,Zr,Li) particles were presented and the recrystallization was restrained. Besides, the trace of dislocations bypassing the Al3(Er,Zr,Li) particles was observed. Herein, the Orowan mechanism was also verified as the main strengthening mechanism of the Al3(Er,Zr,Li) particles by comparing the theoretical value in different strengthening mechanisms with the yield strength. The result demonstrated the impeding effect of the Al3(Er,Zr,Li) particles on the planar slip induced by shearing of the Al3Li, which also corresponded to the disappearance of the plastic instability in the alloy with Er addition. The Al-3Li-1Cu-0.1Zr-0.1Er alloy aged for 56 h possessed better ultimate tensile strength of 306 MPa and yield strength of 235 MPa. Interestingly, this alloy with unremarkable planar slip manifested lower elongation of 9.4% and obvious intergranular fracture when compared to the alloy without Er. To study this specific phenomenon, the hardness of grain interior and grain boundaries was investigated. The result showed that the intergranular fracture of this alloy was induced by higher strength of the grain interior than that of the grain boundaries, while the effect of the traditional planar slip mechanism was not apparent.

Effects of nanosized TiCp dispersion on the high-temperature tensile strength and ductility of in situ TiCp/Al-Cu-Mg-Si nanocomposites

In situ TiCp/Al-Cu-Mg-Si nanocomposites were prepared in Al-Ti-C systems with different carbon sources (pure carbon black, mixed carbon source (50 wt% CNTs + 50 wt% carbon black) and pure CNTs) via a combination of the combustion synthesis, hot press and hot extrusion methods. The in situ TiCp/Al-Cu-Mg-Si nanocomposites synthesized by the mixed carbon source obtained the most uniform distribution of nanosized TiCp, highest yield strength (σ0.2) and tensile strength (σUTS) and best fracture strain (εf). The 30 vol% TiCp/Al-Cu-Mg-Si nanocomposite synthesized by the mixed carbon source showed superior σ0.2 (217 MPa), σUTS (251 MPa), and εf (17.7%) at 533 K, which were respectively 4.3%, 4.1% and 136% higher than those of the nanocomposite synthesized by pure C black (208 MPa, 241 MPa and 7.5%) and respectively 3.8%, 1.6% and 88.3% higher than those of the nanocomposite synthesized by pure CNTs (209 MPa, 247 MPa and 9.4%). The superior high-temperature tensile strength and ductility of the nanocomposites prepared by the mixed carbon source were attributed to the homogeneous distribution of nanosized TiCp. The strengthening of the nanosized TiCp and θ′ precipitates was the main strengthening mechanism of the in situ TiCp/Al-Cu-Mg-Si nanocomposites at high temperatures.

Mechanical strengthening mechanism of Zn-Li alloy and its mini tube as potential absorbable stent material

Pure Zn and Zn-0.5%Li(wt) alloys were cast and extruded into the rods in this study. The micro structure and mechanical properties of Zn, Zn-0.5%Li and its mini tube were evaluated. With the addition of Li, both the UTS and elongation of extruded Zn-0.5%Li alloy increases to 364.9 MPa and 22% compared with Zn. The mini tube made of Zn-0.5%Li alloy shows the UTS of 296.2 MPa and elongation of 33%. The main strengthening mechanism of Zn-Li alloy is attribute to the pinning effects caused by nano LiZn4 precipitates. In conclusion, Zn-Li mini tube could be considered as potential absorbable stent material.

Mechanical properties of Al/ω-Al-Cu-Fe composites synthesized by the SPS technique

Al/40 vol%ω-Al-Cu-Fe composites were produced from Al powder and i-Al-Cu-Fe quasi-crystalline particles using spark plasma sintering (SPS) technique. The mechanical properties of the composite were evaluated over the temperature range 293 K–823 K by performing compression tests at constant strain rate. The temperature dependence of the σ0,2% yield stress gives evidence of two temperature regimes with a transition in the range 473 K–523 K. The decrease of σ0,2% with increasing temperature, more pronounced in the low temperature regime, indicates that the two temperature regimes correspond to two different thermally activated deformation mechanisms. Based on microstructural analyses of the Al matrix, where plastic deformation takes place, the different strengthening contributions are discussed and the results are finally compared to those obtained for composites produced by hot isostatic pressing (HIP), for which the σ0,2% temperature dependence is similar. In the low temperature regime, the σ0.2% stress of the SPS composites is higher than that of the HIP composites. In this temperature regime, the stress difference is mainly ascribed to the different reinforcement phases present in the Al matrix. In the high temperature regime, the temperature dependence of σ0.2% is comparable for the two composites whatever the processing route: load transfer is thus the main strengthening mechanism, which is similar for the two Al/ω-Al-Cu-Fe composites, the temperature dependence being ascribed to cross slip and climb processes.

Exploring the reinforcing effect of TiC and CNT in dual-reinforced Al-matrix composites

Aluminum-matrix composites dual-reinforced by TiC/CNTs were fabricated using a combination of mechanical milling and spark plasma sintering (SPS) techniques. Composition, structure and morphology of the samples were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM). Through TEM, nano-scale uniform distribution of TiC nanoparticles around CNTs was observed. In addition, it was shown that hybridization of TiC nanoparticles with CNTs significantly enhanced the mechanical properties of the dual-reinforced composites. In this regard, improvements of 60% and 33% in nano-hardness as well as 149% and 85% in micro-hardness were achieved by doping 1 wt% TiC/CNT into Al matrix in comparison with pure Al and Al/CNT composite, respectively. Apart from fine ceramic particle strengthening, it was found that CNTs can enhance mechanical properties of Al/CNT composites through their defects, crack-bridging and restriction of dislocations motion. The results showed that the effect of TiC nanoparticles and carbon nanotubes can be considered as a main strengthening mechanism for the dual TiC/CNT reinforced Al composites.

Strengthening mechanism in a high-strength carbon-containing powder metallurgical high entropy alloy

A carbon-containing FeCoCrNiAl0.5 high entropy alloys (HEAs) with high tensile strength was fabricated by powder metallurgy (P/M) method. The P/M process includes gas atomization and hot extrusion of pre-alloyed HEA powder. The microstructural evolution and mechanical properties were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile tests. The results showed that the gas-atomized HEA powder was of dual phase, including face centered cubic (fcc) phase and B2 phase. Hot extrusion caused the precipitation of M23C6 carbides, the formation of dislocations and the refinement of microstructure. The as-extruded HEA exhibited a tensile strength as high as 1093 MPa and an elongation of ∼12.4%. The contributions of different strengthening mechanisms were quantitatively calculated, and it was found that the grain boundary strengthening and the dislocation strengthening are the main strengthening mechanism.

Austenite and precipitation in secondary-hardening ultra-high-strength stainless steel

Ferrium S53 is a new secondary-hardening ultra-high-strength stainless steel, with more Cr than other Co-Ni ultra-high-strength steels. Austenite has a great effect on the fracture toughness of this metal, and the carbides that are precipitated are the main strengthening phase of Ferrium S53 steel; in this study, its microstructural changes during heat treatment were observed and analyzed by X-ray diffraction (XRD), Optical microscope (OM), SEM, and transmission electron microscopy (TEM). About 40.85% retained austenite in the quenched sample is decreased to less than 5% after cryogenic treatment and tempering. In the final sample, block austenite is retained austenite, and film austenite around 5 nm in width is reverted austenite. Inside the martensite lath, parallel twin-like structures are actually segregated M2C precipitates, and most of them are smaller than 20 nm. These precipitates can be aggregated into a several-micron-long parallel zonal microstructure.

Rapid Strengthening Without Loss of Ductility via Electropulsing Treatment in Ti-6Al-4V Alloy

The commercial (hot-rolled and annealed) Ti-6Al-4V alloy subjected to electropulsing was investigated in this study. The results show that the electropulsing-treated sample with optimized parameter exhibits greatly refined microstructure and notable strength improvement without loss of ductility. The main strengthening mechanism is recognized as phase transformation and rapid grain refinement induced by recrystallization under EPT.

Load partition and microstructural evolution during hot deformation of Ti-6Al-6V-2Sn matrix composites, and possible strengthening mechanisms

A Ti-6Al-6V-2Sn alloy reinforced with two different volume fractions of TiC particles was subjected to tensile deformation at 750 °C during in-situ high energy synchrotron diffraction to study the load partition between the α-, β-, and TiC phases. Elastic anisotropies and stress differences are shown for the different phases. Possible strengthening mechanisms are analysed and quantified to explain the differences observed in the peak stresses between the matrix and the composites. TiC particles, with an inhomogeneous distribution within the matrix, are capable of bearing load. Although this can be considered as the main strengthening mechanism, it has negligible effect up to the peak stress of the matrix. The evolution of the microstructure during the hot deformation is also analysed and related to the load partition and the damage of the composite.