FASHS技术制备TiB2+Ni/Ni3Al/405不锈钢梯度材料

采用电场激活自蔓延高温合成(FASHS)技术制备了TiB2 Ni/Ni3Al/405不锈钢梯度材料.试验中首先将镍粉和铝粉球磨处理以促进燃烧反应发生,然后采用FASHS技术利用自蔓延燃烧反应热连接制备了TiB2 Ni/Ni3Al/405不锈钢梯度材料.用SEM和XRD分析了梯度材料各层的界面微观组织及相组成,用洛氏硬度计、显微硬度计及磨料磨损试验机分析了材料的力学性能、硬度及表面抗磨性.结果表明,金属陶瓷复合层、Ni3Al层和405不锈钢金属片间形成了可靠的冶金结合,金属陶瓷复合材料表面硬度为90HRA,材料的化学成分和显微硬度呈梯度分布,耐磨性优于20Cr渗碳钢.     

Influence of thermal treatment on structure and microhardness of Fe75Ni2Si8B13C2 amorphous alloy

Correlation between hardness of amorphous Fe₇₅Ni₂Si₈B₁₃C₂ alloy and thermally induced structural transformations has been investigated by measuring microhardness in a series of samples heated at different temperatures from 25 to 1000 °C. The alloy has a relatively high hardness in the amorphous state, due to its chemical composition involving silicon, boron and carbon. As the alloy begins to crystallize, microhardness increased and reached a plateau in 500–650 °C temperature region, due to formation composite structure involving the small nanocrystals of α-Fe(Si) and Fe₂B phases dispersed in the amorphous matrix. After treatment at higher temperatures, the nanocomposite structure is replaced by a more granulated structure, leading to decline in microhardness.     

二元铝硅合金激光处理显微组织特征

探讨了不同成分的Al-Si二元合金经激光处理后,激光熔区的显微组织特征.讨论了激光熔区的凝固特征及成分与激光熔区的平均显微硬度的关系。     

Structure and magnetic properties of a Ni<Subscript>3</Subscript>(Al,Fe, Cr) single crystal subjected to high-temperature deformation

The structure and magnetic properties of the Ni₃(Al, Fe, Cr) single crystal subjected to high-temperature tensile deformation to failure at 850–900°C have been studied. No recrystallized grains and metastable phases were found. The rupture zone of the alloy subjected to deformation (at 900°C) to the highest degree demonstrates the fragmentation accompanied by rotation of atomic layers and changes of the chemical composition in the nickel and aluminum sublattices. Magnetic studies of the alloy have shown the existence of two Curie temperatures for samples cut from the rupture zone. Samples cut away from the rupture zone exhibit no additional magnetic transitions; twines and planar stacking faults in the alloy structure. The alloy deformed to the lower degree of deformation (at 850°C) also demonstrates twins; no ferromagnetic state was found to form.     

Nano-Borides and Silicide Dispersed Composite Coating on AISI 304 Stainless Steel by Laser-Assisted HVOF Spray Deposition

The study concerned a detailed microstructural investigation of nano-borides (Cr₂B and Ni₃B) and nano-silicide (Ni₂Si) dispersed γ-nickel composite coating on AISI 304 stainless steel by HVOF spray deposition of the NiCrBSi precursor powder and subsequent laser surface melting. A continuous wave diode laser with an applied power of 3 kW and scan speed of 20 mm/s in argon shroud was employed. The characterization of the surface in terms of microstructure, microtexture, phases, and composition were carried out and compared with the as-coated (high-velocity oxy-fuel sprayed) surface. Laser surface melting led to homogenization and refinement of microstructures with the formation of few nano-silicides of nickel along with nano-borides of nickel and chromium (Ni₃B, Cr₂B, and Cr₂B₃). A detailed microtexture analysis showed the presence of no specific texture in the as-sprayed and laser-melted surface of Cr₂B and Ni₃B phases. The average microhardness was improved to 750-900 VHN as compared to 250 VHN of the as-received substrate. Laser surface melting improved the microhardness further to as high as 1400 VHN due to refinement of microstructure and the presence of silicides.     

Vacuum brazing of super-Ni/NiCr laminated composite to Cr18-Ni8 steel with NiCrP filler metal

Vacuum brazing of super-Ni/NiCr laminated composite and Cr18-Ni8 steel was performed using NiCrP filler metal. Microstructure, elemental distribution, microhardness and shear strength were investigated by means of scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electromechanical universal testing machine. An excellent joint was obtained at 1040 °C for 20 min and the shear strength was as high as 137 MPa. The brazed region was divided into solid solution zone and eutectic zone. Elemental distribution indicated that P mainly concentrated in the eutectic zone in the form of Ni₃P. Ni₂Cr particles precipitated in NiCr base layer under the influence of thermal cycling.     

Microstructure and wear resistance of laser-melted TiC reinforced nickel aluminide dual-phase matrix in situ composite

A laser-melted TiC-reinforced nickel aluminide matrix in situ composite was fabricated. The composite consisted of well-developed TiC dendrites and a (NiAl–Ni₃Al) dual-phase matrix. The microstructure of the laser-melted in situ composite was characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that the TiC/(NiAl–Ni₃Al) composite has excellent wear resistance for both room- and high-temperature sliding wear test conditions.     

Structure and yield strength of directionally solidified Ni3Al intermetallic premelted with MoSi2 phase

Ni₃Al and MoSi₂ intermetallic phases were arc melted in Ni₃Al/MoSi₂ molar proportion of ten. Pure binary Ni₃Al and the quaternary alloy were subjected to directional solidification using the floating zone method at growth rates of 10–50 mm h⁻¹. The phase composition and structure of the crystals were analyzed using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. The yield strength was studied in compression at 293–1293 K and in tension at room temperature. Compared to the binary Ni₃Al crystals, the quaternary Ni–Al–Mo–Si crystals revealed up to 5 times higher compressive yield strength at 400–800 K. Ni–Mo–Si C14 Laves phase precipitation in the L1₂ Ni₃Al+L1₀ NiAl matrix duplex phase was found in quaternary crystals. This precipitation is assumed to cause the observed mechanical behaviour.     

Investigation of an as‐sprayed NiCoCrAlY overlay coating – microstructure and evolution of the coating

A low pressure plasma sprayed (LPPS) NiCoCrAlY aircraft turbine blade overlay coating was investigated in the as‐sprayed condition by X‐ray diffraction (XRD) and analytical transmission electron microscopic (TEM) techniques. γ‐Ni, β‐NiAl and γ′‐Ni₃Al phases were identified by XRD showing predominant γ phase at the expense of β phase if compared to the fully processed state with γ and β at about equal portions. Besides grains of γ‐Ni and β‐NiAl, amorphous metallic grains and Cr‐rich oxides were found by TEM. Close to the surface to the atmosphere γ′‐Ni₃Al phase was localized in composite grains with an off‐plane oriented γ‐γ′ fibrous eutectic structure. They were neighbored by amorphous metallic grains. The evolution of these structures is discussed within the scope of crystal growth behavior. The dominant occurrence of face‐centered cubic at the expense of body‐centered phases observed in as‐sprayed coatings is attributed to their higher growth rates on quenching. Also benefiting from rapid growth the γ‐γ′ fibrous eutectic grains will form, hereby relying on essentially binary phase compositions of highly extended solubility ranges. Accumulation of alloy constituents like Cr and Ti by segregation to the growth front is considered to pave the way for the evolution of amorphous grains at the coating surface on top of γ‐γ′ grains. The potentials of the microstructures in service are addressed.     

Rapidly solidified and annealed powders of Ni3Al

Rapidly solidified powders of stoichiometric Ni₃Al and Ni₃Al (B,Ti) were characterized, both as received and after short anneals. Powders generally exhibit spherical morphologies; deviations arise from particle collisions. In the as-received state the stoichiometric Ni₃Al exhibits both lamellar and dendritic structures but the Ni₃Al (B,Ti) contains only dendrites. Only small compositional variations exist across lamellae or dendrites. The as-received powders are only partially ordered. Annealing homogenizes the microstructure and produces strongly ordered structures in which most particles develop large grains. Hardness decreases during annealing. No cracks were found around microhardness indentations on any powders, indicating that Ni₃Al exhibits ductility under compression.     

Crystallisation by laser for Zr based bulk metallic glass

Abstract

Bulk metallic glasses (BMGs) show high amorphous phase stability. The solidification process of BMG occurs with the cessation of epitaxial crystal growth. For a laser heated and melted surface of BMG, crystallisation occurs during cooling, along with crystalline growth from the heat affected zone. Such crystallisation stops at a certain location where the residual melt solidifies as amorphous. The amorphous formation can occur after crystal nucleation. Thermal treatment using a diode laser was used for surface modification of 2 mm thick Zr₅₅Al₁₀Ni₅Cu₃₀ (at.-%) BMG plates. When laser conditions (scanning speed, defocused irradiated spot size and output power) were changed, the maximum temperature and heating cooling rate were changed, and microstructures were changed. Cessation of crystallisation was observed.     

40Cr钢激光表面加Ni60B合金化及其磨蚀性能研究

     对40Cr钢进行了表面加Ni60B粉末激光合金化处理.金相、扫描电镜、X射线衍射分析,硬度测试和磨损与盐雾腐蚀实验的结果表明：合金化层的结构为熔化区、过渡区及热影响区;熔化区显微组织为胞状一树枝状晶,热影响区为极细的隐晶马氏体;激光合金化处理后的试样产生了新相Cr₂₃C₆和Cr₃C2,显微硬度Hk可达到8.6 GPa,比基体提高了近3倍;耐磨性与耐蚀性都比基体有明显提高.       

Influence of thermally induced structural transformations on hardness in Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

Effect of heat treatment on mechanical behavior of Fe_89.8Ni_1.5Si_5.2B₃C_0.5 amorphous alloy was investigated by measuring microhardness. It was shown that the as-prepared amorphous alloy has an unexpectedly high microhardness. This can be attributed not only to boron dispersed in the alloy, but also to the structure which exhibits aspects of a nanocomposite of nanoparticles dispersed in an amorphous matrix. As the alloy crystallizes at temperatures above 540 °C, microhardness decreases continuously as a function of heating temperature. This is attributed to separation of boron out of the amorphous matrix into nanocrystals of Fe₂B phase. Further decrease in microhardness is attributed to crystallite growth with the accompanying change in the dominant nature of the interfaces from amorphous/crystal to crystal/crystal, and creation of a porous structure. When the crystallization is complete, the alloy exhibits microhardness close to that of a hypothetical mixture of α-Fe and Fe₂B phases of the same composition.     

Microstructures,Compressive Properties,and Microhardness of NiAl-Cr(Mo) Eutectic Alloys With Various Ni Contents

The microstructures and mechanical properties of 66(Ni_xAl)-28Cr-6Mo (x?=?1.0, 1.5, 2.0, 2.5, 3.0, and 3.5) alloys were investigated using scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscope, microhardness, and compression tests. The microstructure of NiAl-28Cr-6Mo (Ni_1.0) eutectic alloy consists of NiAl and Cr(Mo) phases. With increasing the Ni content to 2.0, the microstructure changes from eutectic (Ni_1.0) to eutectic?+?primary NiAl dendrite (Ni_1.5 and Ni_2.0), and the morphologies of part of precipitates in primary NiAl dendrite evolve from granular to needle-like. When the Ni content increases further, besides eutectic and primary NiAl dendrite, the gray phase forms and is identified as an ordered FCC (L1₂) (Ni,Cr)₃(Al,Mo) phase. Moreover, the more needle-like precipitates emerge in the primary NiAl dendrite of Ni_2.5, Ni_3.0, and Ni_3.5 alloys, and the precipitate is identified as a bcc Cr(Mo) phase. The deep etching reveals that the three-dimensional morphology of Cr(Mo) precipitate is not needle-like but lath-like. Among the investigated alloys, both Ni_2.0 and Ni_2.5 alloys possess the higher fracture strength and microhardness. The relevant strengthening mechanisms are discussed.     

Corrosion behavior of laser melted AZ91HP magnesium alloy

AZ91HP magnesium alloy was melted by CO₂ laser. Compared with as‐received Mg alloy, the grain of the melted layer was refined significantly and the content of Al was increased. The corrosion resistance of the melted layer was improved because of the grain refinement, the redistribution of β‐Mg₁₇Al₁₂ and the increasing of the Al content. As compared to the non‐overlapping zone, the overlapping zone of the melted layer was liable to be corroded.     

Structure of the Al–Ni intermetallic layers produced on nickel alloy by duplex treatment

Hard and wear and corrosion resistant Al–Ni type intermetallic layers, with an external Al₂O₃ zone, were successfully produced on Inconel 600 using a duplex method. The duplex method combines glow discharge assisted oxidizing with pre-coating the Inconel substrate with aluminum by magnetron sputtering. The oxidizing process carried out at 560 °C for 4 h leads to a diffusion-induced transformation of the aluminum coating and adjacent Inconel into a 15 μm thick composite layer of Al₂O₃+AlNi+AlCr₂+AlNi₃+Cr(Fe,Ni)+Ni(Cr,Fe,Al). The structure of the layer was examined in cross-section by transmission electron microscopy (TEM). The surface zone of the layer is constituted by nanocrystalline Al₂O₃ covering the main zone of the AlNi layer. In this zone, near its border with the oxide zone, are small agglomerates of nanocrystalline Al₂O₃. The upper and thicker part of the AlNi zone also contains precipitates of the AlCr₂ phase. The AlNi zone is separated from Inconel by a diffusion zone of Ni(Cr,Fe,Al). In this region grains of AlNi₃ are found with groups of Cr(Fe,Ni) phase grains. As a consequence, the region is locally strongly enriched with chromium. This suggests that the formation of AlNi induces an uphill diffusion of chromium into the Inconel substrate.     

Comparison of mechanical properties of Ni3Al thin films in disordered FCC and ordered L12 phases

We report the results of several experiments isolating the effect of long-range order on mechanical properties of intermetallic compounds. Kinetically disordered FCC Ni₃Al (Ni 76%) thin films were produced by rapid solidification following pulsed laser melting. For comparison, compositionally and microstructurally identical films with ordered L1₂ structure were produced by subsequent annealing at 550°C for 2 h. These FCC and L1₂ Ni₃Al thin films were tested by nanoindentation for hardness and Young's modulus, and the critical strain to fracture was measured by straining the substrate under four-point bending. Ni₃Al thin films in the disordered phase were found to have nearly twice the critical strain to fracture, more than three times the fracture toughness, and about 20% lower hardness than in the ordered counterpart. Blunter crack tips and crack bridging observed in the disordered phase also illustrate increased ductility. The increased plasticity of Ni₃Al due to chemical disorder is manifested both within the grains and at the grain boundaries. Young's moduli of the ordered and disordered materials were found to be indistinguishable.     

The Effect of Cr on the Lifetime of Al-Rich Amorphous Oxide Layer Formed on Fe–Cr–Al Alloys at 650 °C

The oxidation behavior of Fe–6Al with different Cr contents (0–24 at.%) at 650 °C in air was investigated so as to clarify the role of Cr in the oxidation resistance of the Al-rich amorphous oxide layer. The time to breakdown of the Al-rich amorphous layer was found to increase with increasing alloy Cr content. This corresponds to the time to increase the rate of oxidation by formation of Fe₃O₄. Such a beneficial effect of Cr to maintain the protective Al-rich amorphous layer for a longer oxidation time is attributed to the enhancement of outward diffusion flux of Al by positive “cross-term effect” of Cr in the Al- and Cr-depleted zone.     

Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel

The evolution of precipitates in an Fe–Cr–Ni–Al–Ti stainless maraging steel alloyed with Cu was investigated during aging at 525 °C. Atom probe tomography was used to reveal the development of precipitates and to determine their chemical composition. Two types of precipitates were observed to form during the aging process. Based on their chemical composition these are assumed to be NiAl B2 and Ni₃(Ti,Al) (η-phase). The two phases of precipitates were found to develop independently of each other and the addition of Cu was found to accelerate precipitation. However, the effect of Cu on the nucleation of these phases is different: on the one hand, in the case of NiAl, Cu is incorporated and thus reduces the activation energy by reducing the lattice misfit; on the other hand, Cu acts as a nucleation site for the precipitation of Ni₃(Ti,Al) by forming independent Cu clusters.     

Microstructure,microhardness and corrosion resistance of laser cladding Ni–WC coating on AlSi5Cu1Mg alloy

The microstructure, microhardness, and corrosion resistance of laser cladding Ni–WC coating on the surface of AlSi5Cu1Mg alloy were investigated by scanning electron microscopy, X-ray diffraction, microhardness testing, immersion corrosion testing, and electrochemical measurement. The results show that a smooth coating containing NiAl, Ni₃Al, M₇C₃, M₂₃C₆ phases (M=Ni, Al, Cr, W, Fe) and WC particles is prepared by laser cladding. Under a laser scanning speed of 120 mm/min, the microhardness of the cladding coating is 9–11 times that of AlSi5Cu1Mg, due to the synergistic effect of excellent metallurgical bond and newly formed carbides. The Ni–WC coating shows higher corrosion potential (−318.09 mV) and lower corrosion current density (12.33 μA/cm²) compared with the matrix. The crack-free, dense cladding coating obviously inhibits the penetration of Cl⁻ and H⁺, leading to the remarkedly improved corrosion resistance of cladding coating.