Strengthening and Toughening Effect of Yttrium on Al_(2)O_(3)/TiCN Ceramic Tool Material

The strengthening and toughening effect of yttrium on an advanced Al2O3/TiCN ceramic tool material was studied by means of SEM 9 TEM and energy spectrum analysis. Results showed that yttrium can react with the impurity elements such as W, Fe, Cr, etc. Thus, the interfaces between ceramic phases are purified and the interfacial binding strength is increased. As a result, the mechanical properties of the AL2O3/TiCN ceramic tool material reinforced with yttrium are improved significantly. In addition, the effect of yttrium on particle strengthening of the solid solution TiCN may partly contribute to the improvement of the mechanical properties.

AN INVESTIGATION OF HIGH-TEMPERATURE DEFORMATION STRENGTHENING AND TOUGHENING MECHANISM OF TITANIUM ALLOY

The high-temperature deformation strengthening and toughening mechanisms of titanium alloys have been investigated in this paper. The materials processed by this method produce a new tri-modal microstrvcture, which consists of 10-20% equiaxed alpha, streaky alpha and transformed beta matrix. It is found that the higher ductility of tri-modal microstructure is attributed to the equiaxed alpha's coopemtive slip and coordinated deformation with the transformed beta matrix. The streaky alpha phases not only increase the strength and creep properties, but also increase the fracture toughness. Propagating along grain boundaries between two neighboring streaky alpha phases, cracks in tri-modal microstructure make a more tortuous way, and then the materials show a higher fracture toughness. This new method is applicable to α, near α,α+β and near β titanium alloys.

Ultra-high-temperature application of MXene: Stabilization of 2D Ti_(3)C_(2)T_(x) for cross-scale strengthening and toughening of 3D TiC

Transition metal carbide/nitride cores within MXenes make them considerably useful for ultra-high-temperature reinforcement.However,extensive research on Ti_(3)C_(2)T_(x) MXene has revealed its tendency to undergo a phase transition to TiCy at temperatures above 800℃due to high activity of a superficial Ti atomic layer.Herein,spark plasma sintering of Ti_(3)C_(2)T_(x) and TiC is performed to prevent the Ti_(3)C_(2)T_(x) phase transition at temperatures up to 1900℃through the fabrication of composites at a pressure of 50 MPa.Using a focused ion beam scanning electron microscope to separate layered substances in the composites and examining selected area diffraction spots in a transmission electron microscope enabled identification of non-phase-transitioned MXene.First-principles calculations based on density functional theory indicated the formation of strong chemical bonding interfaces between Ti_(3)C_(2)T_(x) and TiC,which imposed a stability constraint on the Ti atomic layer at the Ti_(3)C_(2)T_(x) surface.Mechanical performance tests,such as three-point bending and fracture toughness analysis,demonstrated that the addition of Ti_(3)C_(2)T_(x) can effectively improve the cross-scale strengthening and toughening of the TiC matrix,providing a new path for designing and developing two-dimensional(2D)carbides cross-scale-enhanced three-dimensional(3D)carbides with the same elements relying on a wide variety of MXenes.

Boron nitride microribbons strengthened and toughened alumina composite ceramics with excellent mechanical,dielectric,and thermal conductivity properties

Aluminum oxide(Al_(2)O_(3))ceramics have been widely utilized as circuit substrates owing to their exceptional performance.In this study,boron nitride microribbon(BNMR)/Al_(2)O_(3)composite ceramics are prepared using spark plasma sintering(SPS).This study examines the effect of varying the amount of toughened phase BNMR on the density,mechanical properties,dielectric constant,and thermal conductivity of BNMR/Al_(2)O_(3)composite ceramics while also exploring the mechanisms behind the toughening and increased thermal conductivity of the fabricated ceramics.The results showed that for a BNMR content of 5 wt%,BNMR/Al_(2)O_(3)composite ceramics displayed more enhanced characteristics than pure Al_(2)O_(3)ceramics.In particular,the relative density,hardness,fracture toughness,and bending strength were 99.95%±0.025%,34.11±1.5 GPa,5.42±0.21 MPa·m^(1/2),and 375±2.5 MPa,respectively.These values represent increases of 0.76%,70%,35%,and 25%,respectively,compared with the corresponding values for pure Al_(2)O_(3)ceramics.Furthermore,during the SPS process,BNMRs are subjected to high temperatures and pressures,resulting in the bending and deformation of the Al_(2)O_(3)matrix;this leads to the formation of special thermal pathways within it.The dielectric constant of the composite ceramics decreased by 25.6%,whereas the thermal conductivity increased by 45.6%compared with that of the pure Al_(2)O_(3)ceramics.The results of this study provide valuable insights into ways of enhancing the performance of Al_(2)O_(3)-based ceramic substrates by incorporating novel BNMRs as a second phase.These improvements are significant for potential applications in circuit substrates and related fields that require high-performance materials with improved mechanical properties and thermal conductivities.

Room-Temperature Mechanical Properties of Rare Earths Reinforced MoSi_2 Material

MoSi 2 and rare earths/MoSi 2 materials were prepared by mechanical alloying, IP and high temperature sintering techniques. Their room temperature properties such as bending strength, fracture toughness and electric conductivity were measured. The results show that rare earths have better strengthening and toughening effects on the MoSi 2 matrix than SiC does. The room temperature bending strength and fracture toughness of 0 9% rare earths/MoSi 2 material are 419 41 MPa and 5 81 MPa·m 1/2 , which have increased by 46% and 81% than the matrix, respectively. The strengthening mechanisms of rare earths/MoSi 2 are fine grain and dispersion strengthening. The toughening mechanisms are fine grain toughening, crack deflection and bowing toughening. Moreover, the effect of rare earths on the electric conductivity of MoSi 2 is much weaker than that of SiC whiskers. With the addition of 0 9% rare earths, the resistivity of MoSi 2 is only raised by about 13 9%.

Refractory high-entropy alloys:A focused review of preparation methods and properties

In recent years,high-entropy alloys(HEAs)have become prominent metallic materials due to their unique design strategies and excellent mechanical properties.The HEAs-inherent high-entropy,lattice-distortion,sluggish-diffusion,and cocktail effects make HEAs maintain high strength,oxidation resistance,corrosion resistance,wear resistance,and other excellent comprehensive properties,showing stronger competitiveness relative to traditional alloys.Refractory high-entropy alloys(RHEAs)are considered as a new kind of high-temperature materials with great application prospects due to their excellent mechanical properties and have the potential to replace nickel-based superalloy as the next generation of high-temperature materials.We reviewed the research status and preparation methods of RHEAs in recent years,including the metallurgical smelting,powder metallurgy,magnetron sputtering,and additive manufacturing technologies.The microstructure and phase-transformation process of RHEAs were analyzed.The mechan-ical properties and main strengthening and toughening mechanisms of RHEAs,such as solid-solution strengthening,precipitation strengthening,and the transformation-induced plasticity(TRIP),were discussed,and the deformation mechanism of RHEAs was revealed.The properties of RHEAs,including high strength,oxidation resistance,corrosion and wear resistance were reviewed.RHEAs will meet the huge market demand in the engineering materials field,but there are still many challenges,such as the tradeoff between high strength and high ductility,structural design,and performance optimization of RHEAs with brittle BCC structures.We believe that this combination of knowledge may shape the future of RHEAs and break through the mutually exclusive conundrum of high strength and high toughness for RHEAs.

Enhanced Strength-Ductility Synergy in Submerged Friction Stir Processing ER2319 Alloy Manufactured by Wire-Arc Additive Manufacturing via Creating Ultrafine Microstructure

Submerged friction stir processing(SFSP)with flowing water was employed to alleviate the porosities and coarse-grained structure introduced by wire-arc manufacturing.As a result,uniform and ultrafine grained(UFG)structure with average grain size of 0.83μm was achieved with the help of sharply reduced heat input and holding time at elevated temperature.The optimized UFG structure enabled a superior combination of strength and ductility with high ultimate tensile strength and elongation of 273.17 MPa and 15.39%.Specifically,grain refinement strengthening and decentralized θ(Al_(2)Cu)phase in the sample subjected to SFSP made great contributions to the enhanced strength.In addition,the decrease in residual stresses and removal of pores substantially enhance the ductility.High rates of cooling and low temperature cycling,which are facilitated by the water-cooling environment throughout the machining process,are vital in obtaining superior microstructures.This work provides a new method for developing a uniform and UFG structure with excellent mechanical properties.

Development and Property Tuning of Refractory High-Entropy Alloys:A Review

In the past decade, multi-principal element high-entropy alloys (referred to as high-entropy alloys, HEAs) are an emerging alloy material, which has been developed rapidly and has become a research hotspot in the fi eld of metal materials. It breaks the alloy design concept of one or two principal elements in traditional alloys. It is composed of five or more principal elements, and the atomic percentage (at.%) of each element is greater than 5%but not more than 35%. The high-entropy eff ect caused by the increase of alloy principal elements makes the crystals easy form body-centered cubic or face-centered cubic structures, and may be accompanied by intergranular compounds and nanocrystals, to achieve solid solution strengthening,precipitation strengthening, and dispersion strengthening. The optimized design of alloy composition can make HEAs exhibit much better than traditional alloys such as high-strength steel, stainless steel, copper-nickel alloy, and nickel-based superalloy in terms of high strength, high hardness, high-temperature oxidation resistance, and corrosion resistance. At present,refractory high-entropy alloys (RHEAs) containing high-melting refractory metal elements have excellent room temperature and high-temperature properties, and their potential high-temperature application value has attracted widespread attention in the high-temperature fi eld. This article reviews the research status and preparation methods of RHEAs and analyzes the microstructure in each system and then summarizes the various properties of RHEAs, including high strength, wear resistance, high-temperature oxidation resistance, corrosion resistance, etc., and the common property tuning methods of RHEAs are explained, and the existing main strengthening and toughening mechanisms of RHEAs are revealed. This knowledge will help the on-demand design of RHEAs, which is a crucial trend in future development. Finally, the development and application prospects of RHEAs are prospected to guide future research.

The simultaneous improvements of strength and ductility in additive manufactured Ni-based superalloy via controlling cellular subgrain microstructure

Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing parameters.During the subsequent homogenization heat treatment process,the Laves phase dispersed at the subgrain boundaries can be eliminated while the cellular subgrain structure is reserved in the printed samples after holding at 1080℃ for 50 min.With the prolongation of the holding time,the subgrain boundaries undergo low angle rotation via the motion ofdislocation,which leads to the annihilation of the cellular subgrain structure.Moreover,during the subsequent double aging heat treatment process,the reserved cellular subgrain structure in the homogenized samples promotes the precipitation of γ" second phase nanoparticles,and these precipitated γ" phase nanoparticles prefer to distribute at subgrain boundaries.It was found that these unique subgrain boundaries with γ" phase precipitates can hinder but not fully terminate the motion of dislocation during the plastic deformation process,which contributes to increasing the strength as well as holding the stable plastic flow.Hence,the strength and ductility of final prepared IN718 alloy with cellular subgrain microstructure were improved simultaneously compared to the prepared alloy without cellular subgrain structure,which even exceed the mechanical properties standards(AMS 5662) of wrought IN718 alloy.These results in our work suggest that controlling the subgrain structure is a promising effective strategy to improve the mechanical properties of SLM manu factured nickel-based superalloy.

Design and preparation of an ultra-high temperature ceramic by in-situ introduction of Zr_(2)[Al(Si)]_(4)C_(5) into ZrB_(2)-SiC:Investigation on the mechanical properties and oxidation behavior

Novel ZrB_(2)-matrix composites were designed and prepared by in-situ introducing SiC and Zr_(2)[Al(Si)]_(4)C_(5) simultaneously for the first time.The obtained composites were dense and showed good mechanical properties,especially the strength and toughness,706 MPa and 7.33 MPa·m^(1/2),respectively,coupled with high hardness of 21.3 GPa,and stiffness of 452 GPa.SiC and Zr_(2)[Al(Si)]_(4)C_(5) constituted a reinforcing system with synergistic effects including grain refinement,grain pull-out as well as crack branching,bridging,and deflection.Besides,the oxidation results of the composites showed that the oxidation kinetics followed the parabolic law at 1600℃,and the oxidation rate constants increased with the increase of Zr_(2)[Al(Si)]_(4)C_(5) content.The formation and evolution model of the oxidation structure was also investigated,and the oxide scale of the composite exhibited a three-layer structure.

Design of Tough, yet Strong, Heat-resistant PLA/PBAT Blends with Reconfigurable Shape Memory Behavior by Engineering Exchangeable Covalent Crosslinks

Polylactide(PLA)has often been blended with biodegradable poly(butylene adipate-co-terephthalate)(PBAT)to improve its toughness.However,the strength and heat resistance of PLA are always sacrificed.Herein,exchangeable hydroxyl-ester crosslinks are constructed in PLA/PBAT blends by successively introducing a tertiary amine-containing polyol,bis-(2-hydroxyethyl)amino-tris(hydroxymethyl)methane(BTM)and 4,4’-diphenylmethane diisocyanate(MDI)via reactive blending.BTM can react with both PLA and PBAT by transesterification,generating PLA or PBAT chains with terminal or pendant hydroxyl groups,which can then react with MDI to form networks.With internal catalysis of tertiary amine moiety in BTM,transesterification between the residual hydroxyl groups and ester bonds can occur at high temperatures,endowing the PLA/PBAT network with vitrimeric properties.Owning to the transesterification and chain extension reactions with MDI between PLA and PBAT,the interfacial adhesion is greatly improved.As a result of the excellent interfacial adhesion and the network structure,the prepared PLA/PBAT blends show greatly enhanced heat resistance and toughness(more than 40 times that of PLA)while maintaining high stiffness comparable to PLA.Furthermore,the prepared PLA/PBAT blends exhibit promising reconfigurable shape memory behavior.The present work provides a new and facile way to achieve high-performance and functional biodegradable polymeric materials.