查看更多>>摘要：High-entropy alloys(HEA)represent a novel material class,with significant potential for research on performance and preparation in additive manufacturing(AM).Currently,FCC HEA dominates the research on AM-fabricated HEA,with a shift in focus from preparation to microstructure design and mechanical properties enhancement.Research on BCC HEA is currently primarily focused on preparation and process optimization.However,it is important to note that the biomedical potential of AM-fabricated BCC HEA should not be overlooked.This review provides a concise summary of the properties and preparation techniques of exceptional HEAs in recent years.It specifically emphasizes the novel microstructure achieved through AM techniques,which significantly enhance the mechanical properties of HEAs.Additionally,the review outlines the various preparation methods employed to mitigate defect introduction during AM processes.Finally,it offers insights into the future research directions and potential applications of additively manufactured HEA.
查看更多>>摘要：Additive manufacturing of β-type titanium alloy is expected to replace Ti-6Al-4V alloy in the field of orthopedic implan-tation because of their low elastic modulus,excellent corrosion resistance,and biocompatibility.After briefly introducing the laser powder bed fusion(LPBF)process and physical phenomena,this paper reviews the recent progresses in LPBF-edβ-type Ti alloys.The strategies to strengthening and toughening β-type Ti alloys are critically reviewed.This is followed by the processing routes employed to achieve to low modulus for orthopedic applications,especially a new methodology for tailoring crystallographic orientation called multi-track coupled directional solidification.The effect of processing and compositions on performance metrics of β-type Ti alloys included corrosion behavior,and biocompatibility is reviewed.In the end,challenges in additive manufacturing of β-type Ti alloys in future are highlighted,with the aim to ensue clinical application of LPBF-ed β-type Ti alloys.
查看更多>>摘要：The metal-based additive manufacturing(AM),also referred to as metal 3D printing,has drawn particular interest because it enables direct creation,aided by computationally-directed path design,of intricate components with site-specific composi-tions and geometrical requirements as well as low buy-to-fly ratios.During the last two decades,the objective of this revolu-tionary technology has been shifting from only"rapid prototyping"to advanced manufacturing of special high-end products or devices,which,in many aspects,outperform conventional manufacturing technologies.For fusion-based AM,significant progress has been achieved in understanding the processing window of macroscopic scales,non-equilibrium metallurgy of mesoscale scales,and grain evolution of microscopic scales.Although the versatile capacity of AM facilitates new avenues for discovering advanced materials and structures,their potential has still not been fully explored.Given the unique non-equilibrium solidification during the AM process,coarse columnar grains with strong textures are usually developed along the build direction,which downgrades the mechanical performance.To push the limits of this digital manufacturing,this review attempts to provide in-depth and comprehensive overviews of the recent progress in understanding the evolution and control of the as-built microstructure that has been made recently and the challenges encountered during the AM process.
查看更多>>摘要：Porous titanium alloy is currently widely used in clinical treatment of orthopaedic diseases for its lower elastic modulus and ability to integrate with bone tissue.At the micro-level,cells can respond to different geometries,and at the macro-level,the geometric design of implants will also affect the biological function of cells.In this study,three kinds of porous scaffolds with square,triangular and circle rod shapes were designed and 3D printed.This study observed the proliferation and differentia-tion of MC3T3-E1 cells during surface culture of the three types of scaffolds.It also evaluated the characteristics of the three scaffolds by means of compression tests and scanning electron microscopy to provide a reference for the design of porous titanium alloy implants for clinical applications.The trends of cell proliferation and gene expression between the three types of scaffolds were observed after treatment with two inhibitors.The results show that the square rod porous scaffolds have the best proliferative and osteogenic activities,and these findings may be due to differences in piezo-type mechanosensitive ion channel component 1(Piezo 1)and Yes-associated protein(YAP)expression caused by the macro-geometric topography.
查看更多>>摘要：The research involves the addition of 5 vol.％TiB2 particles into AA8009 alloy powder to synthesize TiB2/AA8009 composite parts produced via laser powder bed fusion(LPBF).The addition of the TiB2 particles causes the TiB2/AA8009 composites with and without annealing have lower compressive strength than AA8009 alloy due to the change of the strengthening mechanism.The results further indicated that solid solution strengthening was the main strengthening mechanism of the LPBF AA8009 alloy at room temperature whereas Orowan strengthening became the primary strengthening factor after annealing at 673 K.In contrast,Orowan strengthening always remained the main strengthening mechanism for the TiB2/AA8009 composite,irrespective of the annealing temperature.In addition,after annealing of the LPBF parts at 673 K,the compressive yield strength(CYS)of the unblended AA8009 alloy specimens had a～2.5 times greater reduction(from 705±16 to 459±30 MPa)compared to that of the composite TiB2/AA8009 samples(from 466±23 to 368±3 MPa).There-fore,TiB2 particles can suppress the drop in yield strength of LPBF AA8009 alloy below 673 K,providing a theoretical and experimental basis for the applications of both LPBF AA8009 and TiB2/AA8009 alloys at low and medium temperatures.
查看更多>>摘要：The L12-strengthened Co34Cr32Ni27Al4Ti3 medium-entropy alloy(MEA)with precipitations of grain boundaries has been developed through selective laser melting(SLM)followed by cold rolling and annealing,exhibiting excellent strength-ductil-ity synergy.The as-printed alloy exhibits low yield strength(YS)of～384 MPa,ultimate tensile strength(UTS)of～453 MPa,and uniform elongation(UE)of 1.5％due to the existence of the SLM-induced defects.After cold rolling and annealing,the YS,UTS,and UE are significantly increased to～739 MPa,～1230 MPa,and～47％,respectively.This enhancement primar-ily originates from the refined grain structure induced by cold rolling and annealing.The presence of coherent spherical γ'precipitates(L12 phases)and Al/Ti-rich precipitates at the grain boundaries,coupled with increased lattice defects such as dislocations,stacking faults,and ultrafine deformation twins,further contribute to the property's improvement.Our study highlights the potential of SLM in producing high-strength and ductile MEA with coherent L12 nanoprecipitates,which can be further optimized through subsequent rolling and annealing processes.These findings offer valuable insights for the development of high-performance alloys for future engineering applications.
查看更多>>摘要：Porosity is a common phenomenon and can significantly hinder the quality of the coating.Here,the pore formation mecha-nism and the characteristics of the single tracks of the W-C coating using directed energy deposition(DED)are systemati-cally investigated.The forming quality of the tracks,the distribution of the pores,and the elemental distribution near the pores are analyzed by the observations of the cross-sections of the tracks.The temperature field of the melt pool is discussed comprehensively to reveal the pore formation mechanism.The results confirm that Ni and Co evaporated during the DED process due to the high temperature of the melt pool.Pores were continuously produced adjacent to the fusion line when the melt pool was about to solidify since the temperature at the solidification front was higher than the boiling point of Ni.The vaporization area at the fusion line was proposed,where Ni could also evaporate at the time the melt pool started to solidify.The relationship between the solidification rate,the size of the vaporization area and the DED parameters(laser power and scanning speed)was established to discuss the causes of severe pores above the fusion line.This work contains a practical guide to reduce or eliminate the porosity in the coating preparation process on the surface of the tungsten alloy.
查看更多>>摘要：In actual physiological environments,bacteria can activate the immune system and release lactic acid.However,the detailed contribution of lactic acid to the passivation behavior of titanium(Ti)alloys is still unclear.The current work investigated the in vitro passivation behavior of Ti-6Al-4V(TC4)alloys fabricated by laser powder bed fusion in Hank's solution with and without adding lactic acid.Electrochemical methods,inductively coupled plasma atomic emission spectrometer,and X-ray photoelectron spectroscopy were jointly used.Adding lactic acid decreases the corrosion resistance of samples by degrading the formed passive film.The film formed in the(lactic acid)-containing solution exhibits a higher level of oxygen vacancies and a lower thickness,attributed to the suppressed formation of Ti4+transformed from Ti3+and Ti2+.Moreover,the presence of lactic acid would increase the open circuit potential,relieve the ions release,and hinder the deposition of calcium phosphates within 24 h immersion.
查看更多>>摘要：Meeting the damage tolerance requirements for engineering-grade titanium alloys pose a significant challenge in achieving high fracture toughness in direct energy deposition(DED)titanium alloys.This work primarily investigated the relationship between the microstructure and the fracture toughness of DED new Ti-6Al-4V-1Mo alloy.Two types of microstructures were designed via two process strategies:high-line energy density(HE)and low-line energy density(LE).Relative to LE samples,HE samples possess larger-sized microstructural characteristics(coarser grain boundary α(αGB),larger α colonies,and coarser α laths).Less α/β phase boundaries were formed by coarser α laths in the HE samples,increasing the movement of dislocations,resulting in tensile strength decreasing from 1007.1 MPa(LE)to 930.8 MPa(HE)and elongation increasing from 10.8％(LE)to 15.7％(HE).Also,HE samples exhibited an excellent fracture toughness of 114.0 MPa m1/2,significantly higher than that of LE samples(76.8 MPa m1/2).An analysis of crack propagation paths was conducted to investigate the factors contributing to toughening.The primary factor enhancing toughness is the frequent obstruction of cracks by coarseαGB and large α colonies in HE samples.Particularly,the pretty large-angle deflections induced by the superposition effect of coarse αGB and large α colonies play a vital of significant role.These factors induced the long and tortuous high-energy pathways,which resulted in ultimately improved fracture toughness.The discovered microstructural toughening mechanisms can serve as a reference for future studies involving titanium alloys,offering insights on how to enhance fracture toughness by achieving similar characteristics.
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