In-situ deposition of apatite layer to protect Mg-based composite fabricated via laser additive manufacturing

Biodegradable magnesium(Mg) and its alloy show huge potential as temporary bone substitute due to the favorable biocompatibility and mechanical compatibility. However, one issue deserves attention is the too fast degradation. In this work, mesoporous bioglass(MBG)with high pore volume(0.59 cc/g) and huge specific surface area(110.78 m^(2)/g) was synthesized using improved sol-gel method, and introduced into Mg-based composite via laser additive manufacturing. Immersion tests showed that the incorporated MBG served as powerful adsorption sites, which promoted the in-situ deposition of apatite by successively adsorbing Ca2+and HPO42-. Such dense apatite film acted as an efficient protection layer and enhanced the corrosion resistance of Mg matrix, which was proved by the electrochemical impedance spectroscopy measurements. Thereby, Mg based composite showed a significantly decreased degradation rate of 0.31 mm/year. Furthermore,MBG also improved the mechanical properties as well as cell behavior. This work highlighted the advantages of MBG in the fabrication of Mg-based implant with enhanced overall performance for orthopedic application.

Performance-control-orientated hybrid metal additive manufacturing technologies:state of the art,challenges,and future trends

Metal additive manufacturing(AM)technologies have made significant progress in the basic theoretical field since their invention in the 1970s.However,performance instability during continuous processing,such as thermal history,residual stress accumulation,and columnar grain epitaxial growth,consistently hinders their broad application in standardized industrial production.To overcome these challenges,performance-control-oriented hybrid AM(HAM)technologies have been introduced.These technologies,by leveraging external auxiliary processes,aim to regulate microstructural evolution and mechanical properties during metal AM.This paper provides a systematic and detailed review of performance-control-oriented HAM technology,which is categorized into two main groups:energy field-assisted AM(EFed AM,e.g.ultrasonic,electromagnetic,and heat)technologies and interlayer plastic deformation-assisted AM(IPDed AM,e.g.laser shock peening,rolling,ultrasonic peening,and friction stir process)technologies.This review covers the influence of external energy fields on the melting,flow,and solidification behavior of materials,and the regulatory effects of interlayer plastic deformation on grain refinement,nucleation,and recrystallization.Furthermore,the role of performance-control-oriented HAM technologies in managing residual stress conversion,metallurgical defect closure,mechanical property improvement,and anisotropy regulation is thoroughly reviewed and discussed.The review concludes with an analysis of future development trends in EFed AM and IPDed AM technologies.

Characterization of microstructure and strain response in Ti-6Al-4V plasma welding deposited material by combined EBSD and in-situ tensile test

Additive layer manufacturing （ALM） of aerospace grade titanium components shows great promise in supplying a cost-effective alternative to the conventional production routes. Complex microstructures comprised of columnar remnants of directionally solidifiedβ-grains, with interior inhabited by colonies of finerα-plate structures, were found in samples produced by layered plasma welding of Ti-6Al-4V alloy. The application of in-situ tensile tests combined with rapid offline electron backscatter diffraction （EBSD） analysis provides a powerful tool for understanding and drawing qualitative correlations between microstructural features and deformation characteristics. Non-uniform deformation occurs due to a strong variation in strain response between colonies and across columnar grain boundaries. Prismatic and basal slip systems are active, with the prismatic systems contributing to the most severe deformation through coarse and widely spaced slip lines. Certain colonies behave as microstructural units, with easy slip transmission across the entire colony. Other regions exhibit significant deformation mismatch, with local build-up of strain gradients and stress concentration. The segmentation occurs due to the growth morphology and variant constraints imposed by the columnar solidification structures through orientation relationships, interface alignment and preferred growth directions. Tensile tests perpendicular to columnar structures reveal deformation localization at columnar grain boundaries. In this work connections are made between the theoretical macro- and microstructural growth mechanisms and the observed microstructure of the Ti-6Al-4V alloy, which in turn is linked to observations during in-situ tensile tests.

In-situ experiment tests and particulate simulations on powder paving process of additive manufacturing

In this work,in-situ experimental tests are first performed to investigate the powder spreading process of additive manufacturing,where different kinds of scrapers and spreading speeds are employed.Detailed kinetic behaviours of individual powder particles are discussed by discrete element method simulations.It is found that the decrease of inclination angle of the scraper improves the powder pressure and compaction in the spreading process,leading to a denser powder flow and thus a denser powder bed.The increase of spreading speed also improves the powder pressure and compaction in the spreading process.However,the powder flow becomes looser due to the volume dilation,and thus the quality of the paved powder bed decreases.In industrial applications,if the higher powder spreading speed is employed to improve the processing efficiency,the scraper with a smaller inclination angle can be used to ensure the powder bed quality.

Overcoming the limitation of in-situ microstructural control in laser additive manufactured Ti-6Al-4V alloy to enhanced mechanical performance by integration of synchronous induction heating

Although a variety of processing routes were developed to in-situ manipulate microstructure for fabricating high-performance Ti-6Al-4 V alloy by directed energy deposition(DED),the in-situ microstructural control ability has been limited and lead to a narrowed mechanical property control range.This work proved the microstructural correlation betweenβ-grains andα-laths resulting from the unique thermal characteristics of DED for the first time and solved such a dilemma through synchronous induction heating assisted laser deposition(SILD)technology.The results confirmed that the laser energy and inductive energy have a different effect on the solidification and solid phase transformation conditions.By adjusting the laser-induction parameters,the microstructural correlation can be tuned;theβ-grains andα-laths can be controlled relatively separately,thereby significantly enhancing the ductility of as-deposited sample(elongation from 14.2%to 20.1%).Furthermore,the mechanical properties of the tuned microstructures are even comparable to that of DED Ti-6Al-4 V with post heat treatment,which indicates that the potential of SILD to be a one-step manufacturing process to fabricate high performance components without post heat treatment.Furthermore,the tensile testing results of the tuned microstructures indicate thatα-lath size is more influential on the mechanical properties than theβ-grain size due to its stronger hindering effect on the slipping of dislocations.This work promotes the understanding of the microstructural formation mechanism in DED titanium alloy and proves that the combination of synchronous induction and laser can expand the ability to control the microstructure and properties of multi-layer deposition.

Effect of post-heat treatment on Ti_(2)AlNb-based alloy fabricated by twin-wire alternating dual-electron beam additive manufacturing technology

Thanks to its excellent high-temperature performance and moderate density,Ti_(2) AlNb-based alloy is con-sidered to be a new generation of high-temperature structural material in the aerospace field.However,its application is restricted currently due to the limitations of traditional processing methods.Recently,our group first successfully prepared this alloy with an unconventional approach named wire-based in-situ additive manufacturing(AM)technology,and great mechanical performance has been obtained.The unbalanced thermal process of AM easily causes inconsistent or undesired microstructures,as well as mechanical properties.Therefore,in this study,we further carried out post-heat treatment research on the as-printed sample so as to optimize its mechanical performance.Results show that theα2-phase will precipitate from the as-deposited samples(B2/β+O)after solution treatment(ST),while all precipitates were dissolved to the B2/β-matrix when the solution temperature was 1100℃.The aging treatment(AT)promoted a great number of O-phases precipitated and led to an increase in its proportion.With the increase in aging temperature,the tensile strength decreased(995 to 821 MPa)gradually coupling the increase of fracture strain(1.65%to 2.12%),while the aging duration time did not show an obvious ef-fect on its performance.In addition,after proper heat treatment,the high temperature(650℃)tensile strength of the samples was as high as 818 and 792 MPa.This research not only promotes the develop-ment of Ti_(2) AlNb-based alloy fabricated through in-situ AM,but also facilitates its further application in the aerospace field.

Microstructure Evolution and Mechanical Behavior of Laser Melting Deposited TA15 Alloy at 500℃ under In-Situ Tension in SEM

TA15 alloy fabricated by laser melting deposition was investigated at 500℃ under tensile deformation. The damage behavior of microstructure was analyzed by the real time observation of the microstructure evolution, microcracks initiation and propagation using in-situ tensile equipment fitted in the SEM chamber. Finally, the mechanism of fracture was discussed. The result showed anisotropic mechanical properties in X-and Z-direction. The existence of columnar β grains and its orientation to the tensile direction were the major factors inducing the anisotropic mechanical properties. As compared to Z-direction specimen, high tensile strength was observed in X-direction specimen due to the resistance in slips propagation provided by the prior-β grain boundaries( β GBs). Accumulation of the cracks at prior β GB caused the shear fracture. In case of Z-direction specimen, parallel orientation of prior β GB and GB α with the tensile direction resulted in a homogeneous deformation. The high reduction of cross section showed the enhanced ductile characteristics at high temperature.

Development of lunar regolith-based composite for in-situ 3D printing via high-pressure extrusion system

To fully utilize the in-situ resources on the moon to facilitate the establishment of a lunar habitat is significant to realize the long-term residence of mankind on the moon and the deep space exploration in the future.Thus,intensive research works have been conducted to develop types of 3D printing approach to adapt to the extreme environment and utilize the lunar regolith for in-situ construction.However,the in-situ 3D printing using raw lunar regolith consumes extremely high energy and time.In this work,we proposed a cost-effective melting extrusion system for lunar regolith-based composite printing,and engineering thermoplastic powders are employed as a bonding agent for lunar regolith composite.The high-performance nylon and lunar regolith are uniformly pre-mixed in powder form with different weight fractions.The high-pressure extrusion system is helpful to enhance the interface affinity of polymer binders with lunar regolith as well as maximize the loading ratio of in-situ resources of lunar regolith.Mechanical properties such as tensile strength,elastic modulus,and Poisson’s ratio of the printed specimens were evaluated systematically.Especially,the impact performance was emphasized to improve the resistance of the meteorite impact on the moon.The maximum tensile strength and impact toughness reach 36.2 MPa and 5.15 kJ/m2,respectively.Highpressure melt extrusion for lunar regolith composite can increase the effective loading fraction up to 80 wt.% and relatively easily adapt to extreme conditions for in-situ manufacturing.

Microstructure and Mechanical Properties of B-Bearing Austenitic Stainless Steel Fabricated by Laser Metal Deposition In-Situ Alloying

In the field repair application of laser metal deposition(LMD),the kinds of powder materials that can be used are limited,while the equipment components are made of various materials.Hence many components have to be repaired with heterogeneous materials.However,it is difficult to match the mechanical properties between the repaired layer and the substrate due to the diff erent materials.Based on the high flexibility of raw materials and processes in LMD,an in-situ alloying method is proposed herein for tailoring the mechanical properties of LMDed alloy.Using diff erent mixing ratios of Fe314 and 316 L stainless steel powders as the control parameter,the microstructure and mechanical properties of B-bearing austenitic stainless steel fabricated by LMD in-situ alloying with diff erent proportions of Fe314 and 316 L particles were studied.With the increase in the concentration of 316 L steel,the volume fraction of the eutectic phase in deposited B-bearing austenitic stainless steel reduced,the size of the austenite dendrite increased,the yield strength and ultimate tensile strength decreased monotonically,while the elongation increased monotonically.Moreover,the fracture mode changed from quasi-cleavage fracture to ductile fracture.By adding 316 L powder,the yield strength,tensile strength,and elongation of deposited B-bearing austenitic stainless steel could be adjusted within the range of 712 MPa–257 MPa,1325 MPa–509 MPa,and 8.7%–59.3%,respectively.Therefore,this work provides a new method and idea for solving the performance matching problem of equipment components in the field repair.

Review of in-space assembly technologies

With the rapid development of space technology and the increasing demand for space missions,the traditional spacecraft manufacturing,deployment and launch methods have been unable to meet existing needs.In-space assembly(ISA)technologies can effectively adapt to the assembly of large space structures,improve spacecraft performance,and reduce operating costs.In this paper,the development and technologies for ISA are reviewed.ISA is classified from multiple angles,and the research status of ISA is shown clearly through the visual mapping knowledge domain.Then the development status of autonomous robot assembly in the United States,Europe,Japan,Canada and China is reviewed.Furthermore,the key technologies of ISA are analyzed from three aspects:assembly structure design,robot technologies and integrated management technologies.ISA technologies are still facing major challenges and need to be further explored to promote future development.Finally,future development trends and potential applications of ISA are given,which show that ISA will play a vital role in human space exploration in the future.

Rolling-assisted direct energy deposited Inconel 718:Microstructural evolution and mechanical properties after optimized heat treatment

Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance.In this work,the heat treatment strat-egy for Inconel 718 superalloy fabricated by rolling-assisted laser-directed energy deposition(L-DED)has been designed and systematically investigated for the first time.The results show that the designed ho-mogenization heat treatment at 1080℃ for 10 min can effectively dissolve most of the detrimental Lave phases existing in the rolling-assisted L-DED samples.Meanwhile,it results in a homogenous grain struc-ture through static recrystallization,while maintaining a similar prior-refined grain size of∼8μm.On this basis,a high number density ofγ″andγ′precipitates appear in the microstructure after applying a subsequent double-aging heat treatment.The optimized microstructure through such effective post-heat treatment designed in this work has led to a significant increase in material strength at both the room and elevated temperatures while maintaining good ductility.