Rapid additive manufacturing of functionally graded structures using simultaneous wire and powder laser deposition

Laser additive fabrication allows the manufacturing of functionally graded structures that are not possible using conventional subtractive manufacturing. Laser deposition of injected powders with varying compositions, layer-by-layer, is often used for the building up of functionally graded fully dense structures or materials. This approach, however, has some drawbacks: the un-used powders (normally 60-80%) cannot be recycled as they will be contaminated by the powder mixture. In addition, multiple passes are needed to develop functionally graded structures. This paper reports the feasibility and characteristics of using simultaneous powder and wire feeding laser deposition to produce functionally graded structures in a single step. This approach has been shown to eliminate the above problems associated with powder feed laser deposition. In this work, copper powder and nickel wire have been used to deposit functionally grated copper/nickel/iron structures on H13 tool steel. A 1.5-kW diode laser is used for the build-up process. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and optical microscopy are used to analyse the deposited materials in terms of morphology, composition distributions, microstructures and phases formed. Successful deposition of functionally graded Cu-Ni-Fe structures has been demonstrated. Comparisons are made with the dual powder feed deposition process, which shows the inclusion of un-melted Ni powders in the Cu layer as a result of melting temperature difference of the two materials.     

Parametric study of development of Inconel-steel functionally graded materials by laser direct metal deposition

Laser direct metal deposition (LDMD) has developed from a prototyping to a single and multiple metals manufacturing technique. It offers an opportunity to produce graded components, with differing elemental composition, phase and microstructure at different locations. In this work, continuously graded Stainless Steel 316L and Inconel 718 thin wall structures made by direct laser metal deposition process have been explored. The paper considers the effects of process parameters including laser power levels and powder mass flow rates of SS316L and Inconel 718 during the deposition of the Steel–Ni graded structures. Microstructure characterisation and phase identification are performed by optical microscopy and X-ray diffraction techniques. Mechanical testing, using methods such as hardness, wear resistance and tensile testing have been carried out on the structures. XRD results show the presence of the NbC and Fe₂Nb phases formed during the deposition. The effect of experimental parameters on the microstructure and physical properties are determined and discussed. Work shows that mechanical properties can be controlled by input parameters and generation of carbides provides an opportunity to selectively control the hardness and wear resistance of the functionally graded material.     

Laser metal deposition of functionally graded Ti6Al4V/TiC

Functionally graded materials (FGMs) are advanced materials with improved properties that enable them to withstand severe working environment which the traditional composite materials cannot withstand. FGM found their applications in several areas which include: military, medicine and aerospace. Various manufacturing processes are used to produce functionally graded materials that include: powder metallurgy, physical vapour deposition, chemical vapour deposition process and laser metal deposition process. Laser metal deposition (LMD) process is an additive manufacturing process that can be used to produce functionally graded material directly from the three dimensional (3D) computer aided design (CAD) model of the part in one single process. LMD process is a fairly new manufacturing process and a highly non-linear process. The process parameters are of great importance in LMD process and they need to be optimized for the required application. In this study, functionally graded titanium alloy composite was produced using optimized process parameters for each material combination as obtained through a model that was developed in an initial study and the FGM was characterized through metallurgical, mechanical and tribological studies. The results show that the produced FGM has improved properties when compared to those produced at constant processing parameters for all material combinations.     

Functionally graded nickel-aluminide and iron-aluminide coatings produced via laser cladding

Functionally graded nickel-aluminide and iron-aluminide in the form of superimposed clad layers up to 4 mm total thickness were produced on nickel and on iron based substrates, respectively. A continuous wave carbon dioxide laser and two separate powder feeders were employed. The processing parameters were: 1.8 kW laser power, 3 mm beam diameter, and 7 mm s^–1 traverse speed. A series of single clad layers with various Al contents were first produced in order to obtain fundamental data required for the processing of functionally graded materials. Functionally graded Ni-Al and Fe-Al coatings (up to three layers) were produced by successive deposition of clad layers normal to the substrate surface.Compositional control was achieved by keeping the powder flow of Ni or Fe constant and changing the flow rate of Al. Microstructures are interpreted and discussed in relation to aluminides based on the Ni-Al and Fe-Al systems.     

Numerical and experimental study of molten pool behaviour and defect formation in multi-material and functionally graded materials laser powder bed fusion

Laser powder bed fusion (LPBF) of multi-material and functionally graded materials (FGM) has attracted significant research interest due to its ability to fabricate components with superior performance compared with those manufactured with single powder material. However, the forming mechanisms of various defects remain unknown. In this paper, a DEM-CFD model was first established to obtain an in-depth understanding of this process. It was discovered that the defects including partially melted and un-melted Invar36 powder were embedded in the lower level of the powder layer; this was attributed to the low laser absorptivity, low melting point and high thermal conductivity of the Cu10Sn powder. Inter-layer defects were more likely to occur with an increased powder layer thickness. In addition, the scanned track width was found related to an equilibrium achieved among the thermal properties of the powder mixture. Process parameters were optimised to obtain FGM structures without defects in both horizontal and vertical directions. Invar36/Cu10Sn samples were fabricated with a multi-material LPBF system using different mixed powder contents and laser volumetric energy densities (VEDs). By increasing the VED, fewer defects were observed between the interface of two processed powder layers, which had a good agreement with the modelling results.     

金属粉末激光快速成形的工艺及材料成形性

对比了3类金属粉末激光快速成形工艺:选区激光烧结;选区激光重熔,或称选区激光熔覆;以及直接激光沉积,或称激光净成形.提出了其分类依据是金属粉末与激光的作用机制,以及由此导致的金属粉末激光成形机理.综述了上述3类激光快速成形工艺的成形原理、成形材料及工艺优劣,分析了"球化"效应、翘曲变形、以及裂纹等对金属粉末激光成形性的影响规律及相应解决措施.     

电化学研磨法制备超细镍粉

以锂离子电池为微反应器,电化学还原NiO制备了超细镍粉。X射线衍射结果表明所得粉末为纯相Ni,晶粒尺寸约5nm。激光粒度分布测试结果表明Ni粒度分布较窄,中位径集中在200～600nm。透射电镜照片显示颗粒粒径在80～200nm之间;放电电流密度的增加和放电温度的提高都使产物粒径有变大的趋势;在分散过程中加入不同的表面活性剂,可以提高产物Ni的分散性能。     

纯铜/铜合金高反射材料粉末床激光熔融技术进展EI北大核心CSCD

纯铜/铜合金具有优异的导热、导电性能,是重要的工业材料。以粉末床激光熔融为代表的激光增材制造技术具有优良的设计自由度及成形精度,是增材制造的主流发展方向。纯铜/铜合金的粉末床激光熔融与传统加工制造技术相比,前者能够更好地发挥铜优异的性能,在电子电气、汽车、航空航天等导热/导电高需求领域具有广阔的应用前景。本文综述了以纯铜/铜合金为代表的激光高反射材料的粉末床激光熔融的研究现状、面临的重要问题以及相应的解决对策分析。在此基础上,结合本课题组在纯铜/铜合金粉末床激光熔融过程的经验,指出运用蓝光、绿光等短波长激光器进行纯铜/铜合金等高反射材料的粉末床激光熔融是未来的研究热点与发展方向。     

不同晶粒尺寸的三元Cu40Ni40Cr20合金的制备及其显微组织研究

采用电弧熔炼和机械合金化,随后在750℃,58MPa下热压制备了晶粒尺寸差别较大的Cu40Ni40Cr20合金,用X射线衍射仪、扫描电镜等分析手段对比研究了显微组织结构.结果表明:电弧熔炼制备的晶粒尺寸较大的Cu40Ni40Cr20合金为二相,组织极其不均匀;采用机械合金化,通过控制热压条件制备的纳米晶Cu40Ni40Cr20合金仍为双相,但显微组织均匀,稳定.随着球磨时间的延长,由于晶粒细化和应变的结果,衍射峰偏移并有明显的宽化产生,Cu在Cr或Cr在Cu中的固溶度明显增加,当球磨60h后,合金已由双相变成亚稳态的单相.由于机械合金化的粉末处于非平衡态,其超固溶度溶质随热压和真空退火过程的进行会慢慢脱溶分解出来,合金已由单相变为两相,两相颗粒均成倍长大,但仍然保持纳米级尺度;机械合金化、热压和退火后样品中Cu,Ni和Cr的晶格均未发生崎变;讨论了晶粒细化对合金显微组织的影响.     

Microstructure and mechanical properties of TiC-Ni functionally graded materials by simultaneous combustion synthesis and compaction

The simultaneous combustion synthesis and hot compaction of Ti, C and Ni powders under a hydrostatic pressure was undertaken to fabricate fully dense TiC-Ni functionally graded materials (FGM) in a single processing operation. The composition gradient was optimized by finite element analysis and obtained by stacking different powder mixtures of desired compositions. X-ray diffraction, scanning electron microscopy and microprobe analysis were employed to investigate the crystalline phase, microstructure and Ni distribution. Experimental results demonstrate that the combustion reaction was complete and the final products contained the phases TiC and Ni only, the microstructure varies coherently throughout the specimen with no distinct interface. The physical and mechanical properties were measured as a function of composition. It was found that the properties of the FGMs were dependent on the Ni content and approached the maximum values for the relative density, hardness and flexural strength at room temperature when the Ni content was increased to 20 wt%. The maximum in fracture toughness value was found in the TiC-30 wt% Ni material.     

Synthesis of WC hard materials using coated powders

Nickel and cobalt were used as binder materials for tungsten carbide powders (WC) hard materials. Ni and Co binder were added individually to the WC powder by two different methods namely, mechanical mixing and chemical electroless coating. In this study WC powders of grain sizes 0.3–1.0 μm were electroless coated with either nickel or cobalt. The loading of either Ni or Co coating was 13 wt.%. The electroless-coating method conditions of both Ni and Co on WC powders are described. The coated powders were cold compacted and sintered in vacuum at different sintering temperatures. For comparison, identical materials compositions were prepared by mixing the powders constituents mechanically, compacted and sintered under the same conditions.The prepared powders and sintered materials were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that coated WC materials have smaller values of porosity and more homogeneous microstructure while other properties, such as transverse rupture strength, and hardness exhibit greater values than those produced using mixing elemental powders. It is possible to outline the benefits of coated powder approach in the following: high homogeneity and better distribution of binder materials within WC hard materials, higher density and good interfacial bonding, capability of using fine powders, and possibility of using small alloying and/or reinforcement additions in a more uniform manner.     

X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel–copper spinel manganites

The surface of non-stoichiometric nickel and nickel–copper spinel manganites has been investigated by X-ray Photoelectron Spectroscopy (XPS). The oxidation states of the nickel, copper and manganese cations present on the surface of the samples were determined from the analysis of the M 2p_3/2 core levels (M=Ni, Cu, Mn). In particular, both Cu²⁺ and Cu⁺ were evidenced in the structure whereas only bivalent nickel was observed. The partial substitution of manganese by copper led to a chemical shift towards lower binding energy in the Ni 2p_3/2 region, which was explained by the displacement of some Ni²⁺ cations from tetrahedral to octahedral sites of the spinel structure. Finally, the surface atomic ratios Ni/Mn for nickel manganites, Ni/(Mn+Cu) and Cu/(Mn+Ni) for nickel–copper manganites, determined from XPS data, were compared to the ratios corresponding to the bulk composition. This study shows in all cases a nickel enrichment at the surface which is not affected by the copper content of the oxide. On the contrary, the ratio Cu/(Mn+Ni) was found to be lower than the corresponding bulk value.     

Thermodynamics and phase diagrams of lead-free solder materials

Many of the existing and most promising lead-free solders for electronics contain tin or tin and indium as a low melting base alloy with small additions of silver and/or copper. Layers of nickel or palladium are frequently used contact materials. This makes the two quaternary systems Ag–Cu–Ni–Sn and Ag–In–Pd–Sn of considerable importance for the understanding of the processes that occur during soldering and during operation of the soldered devices. The present review gives a brief survey on experimental thermodynamic and phase diagram research in our laboratory. Thermodynamic data were obtained by calorimetric measurements, whereas phase equilibria were determined by X-ray diffraction, thermal analyses and metallographic methods (optical and electron microscopy). Enthalpies of mixing for liquid alloys are reported for the binary systems Ag–Sn, Cu–Sn, Ni–Sn, In–Sn, Pd–Sn, and Ag–Ni, the ternary systems Ag–Cu–Sn, Cu–Ni–Sn, Ag–Ni–Sn, Ag–Pd–Sn, In–Pd–Sn, and Ag–In–Sn, and the two quaternary systems themselves, i.e. Ag–Cu–Ni–Sn, and Ag–In–Pd–Sn. Enthalpies of formation are given for solid intermetallic compounds in the three systems Ag–Sn, Cu–Sn, and Ni–Sn. Phase equilibria are presented for binary Ni–Sn and ternary Ag–Ni–Sn, Ag–In–Pd and In–Pd–Sn. In addition, enthalpies of mixing of liquid alloys are also reported for the two ternary systems Bi–Cu–Sn and Bi–Sn–Zn which are of interest for Bi–Sn and Sn–Zn solders.     

Morphology of ferromagnetic sol–gel submicron silica powders doped with iron and nickel particles

The sol–gel submicron spherical silica particles were obtained with the modified Stöber method using methanol. Iron and nickel dopants produced by the exploding wire method were introduced to the SiO₂ powders during the sol–gel process. The electron microscopy and laser diffraction particle size analyzer studies showed that the hybrid powders agglomerated easily in ethanol. The difference of ζ-potential in pure water between the pure silica (− 46.8 mV), the Fe-doped (− 39.7 mV) and the Ni-doped silica (− 41.5 mV) proved that doping changes the surface properties. The SEM studies confirmed that the Ni-particles could attach to the surface of the silica shells. With TEM it has been found that the differently sized Ni-particles may be encapsulated in silica shells, form clusters within silica or they may remain separate if they were larger than the silica particles. The saturation magnetization of the ferromagnetic hybrid powders was 0.81 emu/g (Fe-doped) and 0.51 emu/g (Ni-doped), while the hysteresis of magnetization revealed that the magnetic particles may have close to a single domain structure. The magnetization values and the X-ray studies confirmed that some Fe-oxides of the initial doping powder remained in the hybrid powder, while the Ni applied was nearly totally metallic.     

单分散镍碳复合纳米球和碳微球的制备

以脱油沥青(deoiled asphalt)为碳源,采用化学气相沉积法(CVD)制备碳微球,其裂解后的残渣经真空热处理制得单分散镍碳复合纳米球.用场发射扫描电镜(FESEM)、高分辨透射电镜(HRTEM)和X射线衍射仪(XRD)对产物进行表征.结果表明,碳微球高纯,属无定型碳结构,大小分布在1～2μm范围内;镍碳复合纳米球为准球形核壳结构,核为镍,壳为碳,尺寸在10～30nm范围,晶化程度较高,结构较完善.     

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.     

Deposition potential dependence of composition, microstructure, and surface morphology of electrodeposited Ni–Cu alloy films

Composition, microstructure, and surface morphology of Ni–Cu alloy films electrodeposited at different deposition potentials have been investigated. The microstructural analysis carried out by using X-ray diffraction (XRD) confirmed that all Ni–Cu films are polycrystalline in nature and possess face-centered cubic structure. XRD analysis also revealed that the (111) peak of the Ni–Cu alloy films splits into two as Cu-rich and Ni-rich peaks and the peak intensities change depending on the deposition potential and hence the film composition. Compositional analysis of Ni–Cu films carried out by energy dispersive X-ray spectroscopy showed that Ni content within the films increases as the deposition potential becomes more negative. The morphological analysis performed by using a scanning electron microscopy and an atomic force microscopy revealed that the surface morphology changes significantly with applied deposition potential. Furthermore, a direct correlation is observed between the surface roughness and lattice strain.     

Fabrication and characterization of NiTi shape memory alloy synthesized by Ni electroless plating of titanium powder

In this work NiTi shape memory alloy was fabricated from mixed elemental powders, Ni plated titanium powder and Ni heated/plated titanium powder by Ar-sintering. Electroless plating process was utilized to fabricate Ni plated titanium powder. For this purpose titanium powder was plated in an electroless Ni bath for 225?min and hydrazine hydrate was used as a reductant to deposit pure nickel on the titanium particles. Ni plated titanium powder was heat treated under an argon atmosphere at 1000?°C to prepare Ni heated/plated titanium powder. Finally, the three sample powders were pressed by CIP followed by sintering at 980?°C for 8?h to manufacture NiTi shape memory alloy. The prepared powders, as well as sintered samples, were characterized by scanning electronic microscopy (SEM), energy dispersive spectrometer analysis (EDS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and differential scanning calorimetric (DSC). The results indicated the presence of NiTi phase and also non-transformable phases (NiTi₂ and Ni₃Ti) in the heated/plated Ti powder and sintered samples. NiTi compound was dominated phase in the heated/plated sintered sample. All three sintered samples, as well as heated/plated powder, showed one-step phase transformation (B2???B19′).     

Microstructure,Properties and Wear Behaviors of (Ni_3Al)_p Reinforced Cu Matrix Composites

Pure copper and its composites reinforced with Ni 3 Al particles were produced by powder metallurgy(PM).Ni 3 Al powders were produced by mechanical ball milling from vacuum arc melted compounds.The Ni 3 Al powders were characterized by X-ray diffraction(XRD).The microscopy examinations revealed that the Ni 3 Al particles were distributed uniformly in the matrix.The effects of the particle fraction on the density,electrical conductivity,strength and dry sliding wear resistance of composite were investigated.It was found that the density and electrical conductivity of the composites decrease while the compression yield strength and wear resistance of composites increase with an increase in the particle fraction.The dry sliding wear tests were performed with pin-on-disk geometry.After sliding wear tests,the worn surfaces were examined by scanning electron microscopy(SEM) equipped with an energy dispersive X-ray spectrometer(EDS).Results have shown that the wear mechanism is oxidative and adhesive.     

超细镍粉的制备及还原生长机理研究

以联氨为还原剂,在硫酸镍水溶液中控制液相还原反应条件制备了超细镍粉,并讨论了超细镍粉的还原生长机理.通过实验分析了工艺参数对还原反应的影响,采用X射线衍射(XRD),扫描电镜(SEM),比表面积测定等分析手段对超细镍粉进行表征,结果表明:超细镍粉的形核和生长独立进行;温度、Ni2+浓度和pH值调控着溶液中镍离子的释放并...