Nickel-based superalloy architectures with surface mechanical attrition treatment: Compressive properties and collapse behaviour

Surface modifications can introduce natural gradients or structural hierarchy into human-made microlattices,making them simultaneously strong and tough.Herein,we describe our investigations of the mechanical properties and the underlying mechanisms of additively manufactured nickel–chromium superalloy(IN625)microlattices after surface mechanical attrition treatment(SMAT).Our results demonstrated that SMAT increased the yielding strength of these microlattices by more than 64.71%and also triggered a transition in their mechanical behaviour.Two primary failure modes were distinguished:weak global deformation,and layer-by-layer collapse,with the latter enhanced by SMAT.The significantly improved mechanical performance was attributable to the ultrafine and hard graded-nanograin layer induced by SMAT,which effectively leveraged the material and structural effects.These results were further validated by finite element analysis.This work provides insight into collapse behaviour and should facilitate the design of ultralight yet buckling-resistant cellular materials.

Low porosity and fine coatings produced by a new type nozzle of high velocity arc spray gun

The new designed high-velocity arc spray gun with three different nozzles is developed to match the DZ400 arc spray system, which can produce the coatings with the structure of superfine and low porosity. This system can be used to spray three normal wires such as 4Cr13, FeCrAl and 7Cr13 （flux cored wires）. Using the scanning electron microscope （ SEM ） to analyze shape and particles size that sprayed by the nozzles with different parameters, as well as with the S-3500N SEM and the energy spectrum analytic （ESA） instrument to identify the content of the oxides, porosity and thickness of the coatings, we get the result that the porosity in the coatings of solid wire is less than 3%, of the flux-cored wires is less than 5%, and the distribution of the coatings sprayed by the nozzle with secondary supplementary airflow is typically shown in the form of highdensity lameUarsplat structure and the average lamellar thickness is around 5μm.

Towards high-strength cold spray additive manufactured metals:Methods,mechanisms,and properties

Cold spray,as a solid-state additive manufacturing process,has been attracting increasing attention from both scientific and industrial communities.However,cold-sprayed deposits generally have unfavorable mechanical properties in their as-fabricated state compared to conventionally manufactured and fusion-based additive-manufactured counterparts due to the inherent microstructural defects in the deposits(e.g.,porosity and incomplete interparticle bonding).This downside reduces its competitiveness and limits its wide applications as an additive manufacturing process.In the past years,many strengthening technologies have been developed or introduced to adjust the microstructure and improve the mechanical properties of cold-sprayed deposits.The term“strengthening”in this work specifically refers to improving the mechanical strength,particularly the tensile strength of the cold-sprayed bulk deposits.According to the stage that the strengthening technologies are used in the cold spray process,they can be classified into three categories:pre-process(e.g.,powder heat treatment),in-process(e.g.,powder heating,in-situ micro-forging,laser-assisted cold spray),and post-process(e.g.,post heat treatment,hot isostatic pressing,hot rolling,friction stir processing).Therefore,a comprehensive review of these strengthening technolo-gies is conducted to illuminate the possible correlations between the strengthening mechanisms and the resultant deposit microstructures and mechanical properties.This review paper aims to help researchers and engineers well understand the different strengthening methods and provide guidance for the cold spray community to develop new strengthening strategies for future high-quality mass production.

In vitro evaluation of Zn-1oMg-xHA composites with the core-shell structure

Zinc-based composites represent promising materials for orthopedic implants owing to their adjustable degradation rates and excellent biocompatibility.In this study,a series of Zn-10Mg-xHA(x=0-5 wt.%)composites with the core-shell structure were prepared through spark plasma sintering,and their microstructural,mechanical,and in vitro properties were systematically evaluated.Results showed that the doped hydroxyapatite(HA)is concentrated at the outer edge of the MgZn2 shell layer.The compression strength of the Zn-1oMg HA composite gradually decreased with the increase of the HA content,while its corrosion rate decreased initially and then increased.The corrosion resistance of the composite with the addition of 1 wt.%HA was improved compared to that of Zn-10Mg-0HA.However,the further increase of the HA content beyond 1 wt.%resulted in a faster degradation of the composite.Moreover,the Zn-10Mg-1HA composite significantly enhanced the activity of Mc3T3-E1 osteoblasts.Based on such findings,it is revealed that the composite containing 1 wt.%HA exhibits superior overall properties and is anticipated to serve as a promising candidate for bone implantmaterials.

Finished surface morphology, microstructure and magnetic properties of selective laser melted Fe-50wt% Ni permalloy

This work focuses on the structure and magnetic properties of Fe-50wt% Ni permalloy manufactured from the pre-alloyed powder by selective laser melting (SLM). The selective laser melted (SLMed) alloys were characterized by a 3D profilometer,optical microscope, scanning electron microscope, X-ray diffraction, etc. The effects of the volume energy density of laser(LVED) on structure, and magnetic properties with coercivity ( H), remanence ( B), and power losses ( P), were evaluated and discussed systematically. The results show that the relative porosity rate and the surface roughness of the SLMed specimens decreased with the increase in LVED. Only the γ-(FeNi) phase was detected in the X-ray diffraction patterns of the SLMed permalloys fabricated from the different LVEDs. Statistical analysis of optical microscopy images indicated that the grain coarsened at higher LVED. Furthermore, the microstructure of the SLMed parts was a typical columnar structure with an oriented growth of building direction. The highest microhardness reached 198 HV. Besides, the magnetic properties including B, H, and Pof SLMed samples decreased when the LVED ranged from 33.3 to 60.0 J/mm ~3 firstly and then increased while LVED further up to 93.3 J/mm, which is related to the decrease in porosity and the increase in grain size, while the higher residual stress and microcracks presented in the samples manufactured using very high LVED. The observed evolution of magnetic properties and LVED provides a good compromise in terms of reduced porosity and crack formation for the fabrication of SLMed Fe-50 wt% Ni permalloy. The theoretical mechanism in this study can offer guidance to further investigate SLMed soft magnetic alloys.

Achieving ultra-high strength and ductility in Mg–9Al–1Zn–0.5Mn alloy via selective laser melting

Fabrication of the Mg–9Al–1Zn–0.5Mn alloy with excellent mechanical performance using selective laser melting(SLM)technology is quite difficult owing to the poor weldability and low boiling point.To address these challenges and seek the optimal processing parameters,response surface methodology was systematically utilized to determine the appropriate SLM parameter combinations.Mg–9Al–1Zn–0.5Mn sample with high relative density(99.5±0.28%)and favorable mechanical properties(microhardness=95.6±5.28 HV_(0.1),UTS=370.2 MPa,and At=10.4%)was achieved using optimized SLM parameters(P=120 W,v=500 mm/s,and h=45μm).Sample is dominated by a random texture and microstructure is primarily constituted by quantities offine equiaxed grains(α-Mg phase),a small amount ofβ-Al_(12)Mg_(17) structures(4.96 vol%,including spherical:[2110]_(α)//[111]_(β)and long lath-like:[2110]_(α)//[115]_(β)or[1011]_(α)//[321]_(β)),and some short rod-shaped Al8Mn5 nanoparticles.Benefiting from grain boundary strengthening,solid solution strengthening,and precipitation hardening of various nanoparticles(β-Al12Mg17 and Al8Mn5),high-performance Mg–9Al–1Zn–0.5Mn alloy biomedical implants can be fabricated.Precipitation hardening dominates the strengthening mechanism of the SLM Mg–9Al–1Zn–0.5Mn alloy.

Additive manufacturing of steel–copper functionally graded material with ultrahigh bonding strength

Additive manufacturing enables processing of functionally graded materials(FGMs)with flexible spatial design and high bonding strength.A steel-copper FGM with high interfacial strength was developed using laser powder bed fusion(LPBF).The effect of laser process parameters on interfacial defects was evaluated by X-ray tomography,which indicates a low porosity level of 0.042%therein.Gradient/fine dendritic grains in the interface are incited by high cooling rates,which facilitates interface strengthening.Multiple mechanical tests evaluate the bonding reliability of interface;and the fatigue tests further substantiate the ultrahigh bonding strength in FGMs,which is superior to traditional manufacturing methods.Mechanisms of the high interfacial bond strength were also discussed.

Pressure infiltration of molten aluminum for densification of environmental barrier coatings

Environmental barrier coatings(EBCs)effectively protect the ceramic matrix composites(CMCs)from harsh engine environments,especially steam and molten salts.However,open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives,and lead to premature failure of EBCs.This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings.These results showed that it was difficult for aluminum to infiltrate spontaneously,but with the increase of external gas pressure and internal vacuum simultaneously,the molten aluminum obviously moved forward,and finally stopped infiltrating at a depth of a specific geometry.Based on the wrinkled zigzag pore model,a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established.The infiltration results confirmed this relationship,indicating that for a given coating,a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration.

A novel laser shock post-processing technique on the laser-induced damage resistance of 1ωHfO_(2)/SiO_(2)

The laser shock processing implemented by a laser-induced high-pressure plasma which propagates into the sample as a shockwave is innovatively applied as a post-processing technique on HfO_(2)/SiO_(2) multilayer coatings for the first time.The pure mechanical post-processing has provided evidence of a considerable promotion effect of the laser-induced damage threshold,which increased by a factor of about 4.6 with appropriate processing parameters.The promotion mechanism is confirmed to be the comprehensive modification of the intrinsic defects and the mechanical properties,which made the applicability of this novel post-processing technique on various types of coatings possible.Based on experiments,an interaction equation for the plasma pressure is established,which clarifies the existence of the critical pressure and provides a theoretical basis for selecting optimal processing parameters.In addition to the further clarification of the underlying damage mechanism,the laser shock post-processing provides a promising technique to realize the comprehensive and effective improvement of the laser-induced damage resistance of coatings.

Progress in ceramic materials and structure design toward advanced thermal barrier coatings

Thermal barrier coatings(TBCs)can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat.However,the continuous pursuit of a higher operating temperature leads to degradation,delamination,and premature failure of the top coat.Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems.In this paper,the latest progress of some new ceramic materials is first reviewed.Then,a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth,ceramic sintering,erosion,and calcium–magnesium–aluminium–silicate(CMAS)molten salt corrosion.Finally,new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar,columnar,and nanostructure inclusions.The latest developments of ceramic top coat will be presented in terms of material selection,structural design,and failure mechanism,and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance,better thermal insulation,and longer lifetime.

Al-modification for PS-PVD 7YSZ TBCs to improve particle erosion and thermal cycle performances

Plasma spray-physical vapor deposition(PS-PVD)as a novel process was used to prepare feather-like columnar thermal barrier coatings(TBCs).This special microstructure shows good strain tolerance and non-line-of-sight(NLOS)deposition,giving great potential application in aero-engine.However,due to serious service environment of aero-engine,particle erosion performance is a weakness for PS-PVD 7YSZ TBCs.As a solution,an Al-modification approach was proposed in this investigation.Through in-situ reaction of Al and ZrO2,anα-Al2O3 overlay can be formed on the surface of 7YSZ columnar coating.The results demonstrate that this approach can improve particle erosion resistance since hardness improvement of Al-modified TBCs.Meanwhile,as another important performance of thermal cycle,it has a better optimization with 350-cycle water-quenching,compared with the as-sprayed TBCs.