Microstructural and mechanical properties investigation of electrodeposited and annealed LIGA nickel structures

Lithographic, Galvanoformung, Abformung (LIGA) component fabrication is a process in which structural material is deposited into a patterned polymethyl-methacrylate (PMMA) mold realized through deep X-ray lithography. The process permits fabrication of metal microelectrome chanical systems (MEMS) components with representative dimensions that range from a few microns to several millimeters. This investigation characterizes the microstructure and mechanical properties of LIGA-fabricated nickel (LIGA Ni), electrodeposited using Watts bath and sulfamate bath chemistries. As a prelude to studying high-temperature joining processes in LIGA Ni components, an annealing investigation was conducted on samples fabricated from both bath chemistries. Mechanical properties and microstructural analyses on as-deposited and annealed samples were conducted using a mini servohydraulic load frame and the electron backscatter diffraction (EBSD) microtexture measurement technique. The deposits were found to have fine-grain, highly textured microstructures oriented with an acicular or columnar morphology relative to the plating direction. Previously uncharacterized, anomalous, local spatial variations in the crystallographic texture of the as-deposited microstructures were identified by EBSD analyses. Microstructural evolution during annealing seemed to follow a recovery, recrystallization, rapid grain-growth microstructural-evolution mechanism in LIGA Ni deposited from the Sulfamate bath chemistry and simply a recovery and grain-growth microstructural-evolution mechanism in LIGA Ni deposited from the Watts bath chemistry. The evolution of microstructure in the annealed samples corresponded with a dramatic drop in their strength and determined the limiting diffusion-bonding temperature for LIGA Ni components.     

Enhancing physical and mechanical properties of Mg using nanosized Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particulates as reinforcement

A magnesium-based composite with 1.1 volume percentage of nanosized Al₂O₃ particulates reinforcement was fabricated using an innovative disintegrated melt deposition technique followed by hot extrusion. Al₂O₃ particulates with an equivalent size of 50 nm were used as reinforcement. Microstructural characterization of the materials revealed grain refinement of magnesium matrix due to incorporation, retention, and uniform distribution of reinforcement. Physical properties characterization revealed that the addition of nano-Al₂O₃ particulates as reinforcement improves the dimensional stability of pure magnesium. Mechanical properties characterization revealed that the presence of nano-Al₂O₃ particulates as reinforcement leads to a significant increase in microhardness, dynamic elastic modulus, 0.2 pct yield strength (YS), ultimate tensile strength (UTS), and ductility of pure magnesium. The results revealed that the combined tensile properties of these materials are superior when compared to Mg reinforced with much higher volume percentage of SiC. An attempt is made in the present study to correlate the effect of nano-Al₂O₃ particulates as reinforcement with the microstructural, physical, and mechanical properties of magnesium.     

Investigation of Microstructure,Mechanical and Wear Behaviour of B<Subscript>4</Subscript>C Particulate Reinforced Magnesium Matrix Composites by Powder Metallurgy

In the present study, magnesium and magnesium matrix composites reinforced with 10, 20 and 30 wt% B₄C particulates were fabricated by powder metallurgy using hot pressing technique. The microstructure, mechanical properties and wear behaviour of the samples were investigated. Microstructure characterization showed generally uniform distribution of B₄C particulates. XRD investigations revealed the presence of Mg, B₄C and MgO phases. The mechanical properties of the investigated samples were determined by hardness and compression tests. Hardness and compressive yield strength significantly increased with increasing B₄C content. The reciprocating wear tests was applied under loads of 5, 10 and 20 N. Wear volume losses decreased with increasing B₄C content. Abrasive and oxidative wear mechanisms were observed.     

Effect of nano-SiC content on mechanical properties of SiC/2014Al composites fabricated by powder metallurgy combined with hot extrusion

Nano-SiC particulates (n-SiC_p) reinforced 2014Al matrix composites with different reinforcement volume fractions (0, 0.25, 0.5 and 1?vol.-%) were fabricated by powder metallurgy combined with hot extrusion. The effect of volume fraction of n-SiC_p on mechanical properties of composites was studied at both ambient and elevated temperatures. The increase of n-SiC_p content led to an increase in yield strength (YS) and ultimate tensile strength (UTS) and a slight decrease in elongation which is much better than the composites reinforced with micro-SiC_p. The 0.5?vol.-% n-SiC_p/2014Al composite observed the highest YS and UTS of ～378 and ～573?MPa at room temperature and of ～303 and ～409?MPa at 473?K. The enhancement of the properties is suggested to be induced by uniformly dispersed and well-bonded n-SiC_p reinforcements as well as the age-hardening effect of the more and finer precipitates.     

Effects of Cr Reduction on High-Temperature Strength of High-Ni Austenitic Cast Steels Used for High-Performance Turbo-chargers

Since greater high-temperature strength is required for maintaining high-performance turbo-chargers at higher exhaust gas temperatures, e.g., 1323 K (1050 °C), high-Ni (20 wt pct) austenitic steel (ASTM HK40 steel) is presented as an excellent turbo-charger candidate material. To enhance the strength, three types of austenitic cast steel were fabricated in this study by controlling the Cr content in HK40 steel, and high-temperature strength improvement was achieved by detailed microstructural evolution including carbide formation and matrix strengthening. Room temperature and high-temperature strengths were expected to be proportional to the carbide volume fraction, but revealed an opposite trend because the steel containing more Cr (having more carbides) revealed lower strength than the steel containing less Cr (having fewer carbides). This result was associated mainly with the M₇C₃ to M₂₃C₆ decomposition occurring at high temperatures in the less-Cr-steel that beneficially strengthened the austenite matrix and reduced the hardness difference between the carbide and matrix, consequently improving the high-temperature strength. In considering the alloying prices (14 pct cost saving of alloying elements) as well as the high-temperature strength, the steel containing less Cr is promising for new high-performance turbo-charger applications.

     

In Situ ceramic particle-reinforced aluminum matrix composites fabricated by reaction pressing in the TiO2 (Ti)-Al-B (B2O3) systems

Particulate TiB₂ reinforced aluminum-based metal matrix composites (MMCs) were successfully fabricated by means of the reaction processing method. TiB₂ particulates were formed in situ through the reaction of Ti and B in Ti-Al-B, TiO₂ and B in TiO₂-Al-B, and TiO₂ and B₂O₃ in TiO₂-Al-B₂O₃ systems. The results showed that in situ TiB₂ particulates formed in the Ti-Al-B system had a size of 5 μm and they exhibited block and rodlike structures. Moreover, coarse Al₃Ti blocks several tens of micrometers in size were also formed simultaneously. On the other hand, equiaxed Al₂O₃ and TiB₂ particulates with a size of less than 2 μm were formed in situ in the TiO₂-Al-B and TiO₂-Al-B₂O₃ systems. The Al₃Ti phase was completely eliminated in the TiO₂-Al-B system with increasing B content. Tensile tests revealed that the Al₂O₃ · TiB₂/Al composite fabricated from the TiO₂-Al-B system exhibits excellent mechanical properties. The yield strength of the Al₂O₃ · TiB₂/Al composite appeared to increase with increasing TiB₂ content. The yield strength of the Al₂O₃ · TiB₂/Al composite could be further increased by introducing CuO into the TiO₂-Al-B system. Such an increment in mechanical strength arose from the strengthening effect caused by the Al₂Cu precipitates. The incorporation of CuO had no effect on the in situ reaction process of the TiO₂-Al-B system. Finally, the effect of SiC addition on the microstructure and mechanical properties of the composites fabricated from the TiO₂-Al-B and TiO₂-Al-B-CuO systems was also investigated.     

Hot Extrusion of A356 Aluminum Metal Matrix Composite with Carbon Nanotube/Al2O3 Hybrid Reinforcement

Over the years, the attention of material scientists and engineers has shifted from conventional composite materials to nanocomposite materials for the development of light weight and high-performance devices. Since the discovery of carbon nanotubes (CNTs), many researchers have tried to fabricate metal matrix composites (MMCs) with CNT reinforcements. However, CNTs exhibit low dispersibility in metal melts owing to their poor wettability and large surface-to-volume ratio. The use of an array of short fibers or hybrid reinforcements in a preform could overcome this problem and enhance the dispersion of CNTs in the matrix. In this study, multi-walled CNT/Al₂O₃ preform-based aluminum hybrid composites were fabricated using the infiltration method. Then, the composites were extruded to evaluate changes in its mechanical properties. In addition, the dispersion of reinforcements was investigated using a hardness test. The required extrusion pressure of hybrid MMCs increased as the Al₂O₃/CNT fraction increased. The deformation resistance of hybrid material was over two times that of the original A356 aluminum alloy material due to strengthening by the Al₂O₃/CNTs reinforcements. In addition, an unusual trend was detected; primary transition was induced by the hybrid reinforcements, as can be observed in the pressure–displacement curve. Increasing temperature of the material can help increase formability. In particular, temperatures under 623 K (350 °C) and over-incorporating reinforcements (Al₂O₃ 20 pct, CNTs 3 pct) are not recommended owing to a significant increase in the brittleness of the hybrid material.     

Microstructure,Thermal, Thermo-mechanical and Fracture Analyses of Hybrid AA2024-SiC Alloy Composites

This research work aims to investigate the inter-correlation between microstructure, thermal (thermal conductivity, thermo-gravimetric analysis), thermo-mechanical (dynamic mechanical analysis) and fracture characteristics of hybrid AA2024-SiC alloy composites fabricated via semi-automatic stir-casting process, as per standard industrial practice. Silicon Carbide (SiC) particulates of varying amount (0–6 wt%; @ step of 2%) were used to reinforce master batch of AA2024 wrought alloy, Silicon Nitride (Si3N4) and graphite particulates. The thermal conductivity and storage-modulus magnitudes of alloy composites have shown diminishing trend with hard SiC reinforcing phase, while material stability, viscous modulus, damping factor and fracture toughness have shown significant improvement. Uniform dispersion and better interfacial adhesion between matrix–reinforcement were observed from metallographic examination. The XRD analysis identified the different phases of the hybrid alloy composites. The trends in variations of physical, mechanical and tribological properties were supported by microstructure analysis, thermal analysis, thermo-mechanical analysis and fracture analysis.     

Mechanical properties of NiAl-Y2O3-based powdered alloys produced by directional recrystallization

The mechanical properties of NiAl-Y₂O₃-based powdered composite alloys (0.5–7.5 vol %), including those with an NiAl intermetallic matrix alloyed with 0.5 wt % Fe and 0.1 wt % La have been studied. Structures with various aspect ratios (AR, the ratio of the grain length to the grain diameter) are formed using deformation and subsequent annealing. A combination of the optimum amount of strengthening phase (2.5 vol % Y₂O₃) and a quasi-single-crystalline structure with a sharp axial texture with the (100) main orientation and AR ≈ 20–40 provides the maximum short-term strength and life at temperatures up to 1400–1500°C. An NiAl-Y₂O₃ alloy (2.5 vol %) has the best strength properties among all known nickel superalloys at temperatures higher than 1200°C and can operate under moderate loads at temperatures higher than the working temperatures of nickel superalloys (by 100–400°C) and their melting points. Additional alloying with 10 wt % Co and 2 wt % Nb makes it possible to increase the ultimate tensile strength of an intermetallic NiAl matrix at 1100°C by a factor of 1.3–1.4.     

Nickel and cobalt eutectic alloys reinforced by refractory metal carbides

Eutectiferous behavior was observed within pseudobinary joins between the monocarbides of the group IVa and Va metals with nickel and cobalt. Coupled two phase growth normal to a macroscopically planar liquid-solid interface was noted even though the various carbide phases grew in a faceted manner. The composite structures formed by unidirectional freezing consisted of either a cobalt or nickel matrix with an aligned whisker-like or three-sided lamellar carbide dispersion. The nickel-niobium monocarbide system was examined in greatest detail and found to be stronger than TD nickel in tension from room temperature to 2100°F. Repeated fracture along the length of individual carbide whiskers was observed during tensile straining. This behavior, which is nontypical of previous eutectic whisker composites, was interpreted in terms of the distribution in whisker strengths. The strength of extracted NbC whiskers measured in bending was found to approach the theoretical failure stress. Creep rupture tests further indicated that reinforcement of a weak nickel or cobalt matrix with aligned monocarbide whiskers provides a new type of material for use at elevated temperatures.     

Ni–ZrO2 Composite Coating by Electro-Co-Deposition

In the present investigation Ni–ZrO₂ metal matrix composite coatings were prepared on steel substrate using watt’s type solution through electro-co-deposition process with different weight percentages of zirconia powder dispersed in the bath. In the coating, nickel is present with faceted appearance along with ZrO₂. The microhardness and wear resistance of the coatings increase with increasing weight percentage of particles content in the coating. The hardness of the resultant coatings was found to be 325 VHN for pure Ni coating whereas 401VHN for Ni–ZrO₂ (15 g/l ZrO₂) coating depending on the particle volume in the Ni matrix. The results also showed that the wear resistance of the composite coatings was improved as compared to unreinforced Ni deposited material. Strengthening of the coating was attributed to the ZrO₂ dispersion and partially favorable texture.     

Structure and properties of a rapidly solidified Al-Li-Mn-Zr alloy for high-temperature applications: Part II. spray atomization and deposition processing

A new Al-Li alloy containing 2.3 wt pct Li, 6.5 wt pct Mn, and 0.65 wt pet Zr for high-temperature applications has been processed by a rapid solidification (RS) technique (as compacts by spray atomization and deposition) and then thermomechanically treated by hot extrusion. As-received and thermomechanically treated deposits were characterized by X-ray diffraction and scanning electron microscopy (SEM). Phase analyses in the as-processed materials revealed the presence of two Mn phases (Al₄Mn and Al₆Mn), one Zr phase (Al₃Zr), two Li phases (the stable AlLi and the metastable Al₃Li), and the aAl solid solution with high excess in Mn solubility (up to close the nominal composition in the as-atomized powders). As-deposited and extruded pieces were given heating treatments at 430 °C and 530 °C. A two-step aging treatment was practiced, to check for the optimal (for tensile properties) aging procedure, which was found to be the following: solutioning at 430 °C for 1 hour and water quenching + a first-step aging at 120 °C for 12 hours + a second-step aging at 175 °C for 15 hours. The mechanical properties, at room and elevated temperatures, of the hot extruded deposits are compared, following the optimal solutioning and aging treatments. The room-temperature (RT) strength of the proposed alloy is distinctly better for the as-deposited specimens (highest yield strength, 320 MPa) than for the as-atomized (highest yield strength, 215 MPa), though less than 65 pct of the RT strength is conserved at 250 °C. Ultimate strengths are quite comparable (in the 420 to 470 MPa range). Ductilities at RTs are in the low 1.5 to 2.5 pct range and show no improvement over other Al-Li alloys.     

Studies on the effect of processing parameters on electroless coating of copper on boron carbide particles

Boron carbide a hard refractory semiconductor ceramic material due to its unique structural properties and high neutron cross section finds application as structural materials and neutron shielding material. Its applicability is reduced due to low sinterbility and dispersiblity which can be overcome by copper coating. The effect of Electroless coating parameters on the surface deposits is characterised. The studies revealed that uniform and smooth coating was observed for pH11 at bath temperature of 348K. The prolonged suspension of B₄C particles on the reaction bath has little effect on coating but it inturns reduces the adhesion of coating on activated particles.     

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

The mechanical properties of aluminum-graphite composites were measured at room temperature in the as-received condition, after elevated temperature exposure and after thermal cycling. The composites were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers. The results showed that the maximum longitudinal tensile strength of the as-received material was 80,000 psi (552 MN/m²), which corresponds well with the rule of mixture value. The composite strength was observed to vary widely, depending on the extent of wetting of the fibers by the aluminum. The strength of the composites in the transverse direction was generally very low, due to poor interfacial bonding. Aluminum carbide (A1₄C₃) formed at the surface of the fibers at temperatures greater than 500‡C (773 K). Development of the carbide was shown to be diffusion-controlled and was dependent on the time and temperature used. It was shown that the tensile strength was virtually unaffected by heat-treatment up to 500‡C (773 K); beyond that temperature a drastic degradation of tensile strength occurred. The degradation could be correlated with the extent of carbide development at the interface. Thermal cycling of the composites below 500‡C (773 K) resulted in an observable degradation of the composite strength. Scanning electron microscopy of fractured surfaces indicated that the relatively weak interface governs the mode of failure in tension.     

Study on the Structures and Properties of Ni-W-B-CeO2 Composite Coatings Prepared by Pulse Electrodeposition

The aim of this research is to pulse co-deposit nano-CeO2 particles into Ni-W-B alloy coatings in order to improve the surface properties. The influence of pulse frequency and duty circle on deposition rate, microhardness and microstructures, and the influence of heat treatment temperature on phase structures, microhardness and abrasivity of Ni-W-B-CeO2 composite coatings were investigated. The results indicated that the pulse co-deposition of nickel, tungsten, boron and nano-CeO2 particle from the bath which nano-CeO2 particle was suspended by high speed mechanical stirring led to the Ni-W-B-CeO2 composite coatings, possessing better microhardness and abrasion resistance when heat-treated at 400℃ for 1h. The microhardness as-deposited with 636Hz and the deposition rate with 0.0281mm·h-1 was the highest at pulse frequency with 1000Hz and pulse duty circle with 10%. Microstructures analysis displays that decreasing pulse duty cycle leads to refinement in grain structures and the improvement of microstructures. X-ray diffraction shows that the composite coating as-deposited was mainly in the amorphous state and partially crystallized, but when heat treated at 400℃, the crystallization trend was strenthened further.     

激光熔化沉积Rene95镍基高温合金的凝固组织及力学性能

采用激光熔化沉积方法制备出Rene95镍基高温合金薄壁样, 分析了沉积态的凝固组织, 并进行了热处理和力学性能测试. 研究表明, 激光熔化沉积Rene95镍基合金的凝固组织为外延生长的定向凝固组织, 其一次枝晶间距在20 μm左右, 二次枝晶臂细小甚至退化, 元素偏析较轻; 通过适当的热处理后, 合金中γ′沉淀相的体积分数明显增加, 合金的显微硬度由沉积态的HV_(0.1) 500提高到HV_(0.1) 540; 经过热处理后, 激光熔化沉积Rene95合金的室温抗拉强度为1247 MPa, 较粉末冶金C级水平略低, 而沿沉积高度方向的延伸率为16.2%, 高于粉末冶金A级水平.     

Substructure strengthening in dispersion-strengthened nickel alloys

Pure nickel, 80 pct Ni-20 pct Cr, 98 pct Ni-2 pct ThO₂, and 78 pct Ni-20 pct Cr-2 pct ThO₂ were studied in a wide range of thermomechanical conditions to identify strengthening mechanisms in the dispersion-strengthened materials. An X-ray line profile technique was used to determine the distribution of lattice strain, the crystallite domain size and the incidence of twins and stacking faults. Transmission electron microscopy was carried out, and tensile tests were done at room temperature and at an elevated temperature. It was found that cold deformation of Ni?ThO₂ did not produce lattice strains as large as was the case with pure nickel and Ni?Cr. However, deformation of Ni?Cr?ThO₂ did generate high lattice strains, due it is thought to the influence of chromium on cross-slip. The materials containing high lattice strains recrystallized more readily on annealing or testing at high temperature. It was concluded that room temperature strength was related to domain size without regard to composition in the series investigated. Strengthening by particle-dislocation interaction was not thought to be applicable when the domain size was small compared to the interparticle spacing, or at elevated temperatures. High temperature strength was determined primarily by the presence of a polygonized dislocation substructure which was stabilized by the thoria dispersion.     

High-temperature mechanical behavior of Ti-6Al-4V alloy and TiC p /Ti-6Al-4V composite

Mechanical behaviors at 538 °C, including tensile and creep properties, were investigated for both the Ti-6Al-4V alloy and the Ti-6Al-4V composite reinforced with 10 wt pct TiC particulates fabricated by cold and hot isostatic pressing (CHIP). It was shown that the yield strength (YS) and ultimate tensile strength (UTS) of the composite were greater than those of the matrix alloy at the strain rates ranging from approximately 10⁻⁵ to 10⁻³ s⁻¹. However, the elongation of the composite material was substantially lower than that of the matrix alloy. The creep resistance of the composite was superior to that of the matrix alloy. The data of minimum creep strain rate vs applied stress for the composite can be fit to a power-law equation, and the stress exponent values of 5 and 8 were obtained for applied stress ranges of 103 to 232 MPa and 232 to 379 MPa, respectively. The damage mechanisms were different for the matrix alloy and the composite, as demonstrated by the scanning electron microscopy (SEM) observation of fracture surfaces and the optical microscopy examination of the regions adjacent to the fracture surface. The tensile-tested matrix alloy showed dimpled fracture, while the creep-tested matrix alloy exhibited preferentially interlath and intercolony cracking. The failure of the tensile-tested and creep-tested composite material was controlled by the cleavage failure of the particulates, which was followed by the ductile fracture of the matrix.     

Influence of sintering conditions on tensile and high cycle fatigue behaviour of powder injection moulded Ti–6Al–4V at ambient and elevated temperatures

Abstract

Tensile and high cycle fatigue properties of Ti–6Al–4V samples fabricated by powder injection moulding (PIM) are examined at room temperature and elevated temperatures. Standard wrought Ti–6Al–4V material is used for comparison. The tensile and the fatigue strength of samples fabricated by powder injection moulding are found to be significantly lower than conventional wrought material. On the other hand, strength and ductility of metal injection moulded (MIM) samples are high enough to be of large practical interest, in particular if the low processing costs for intricate shapes are taken into account. The inferior properties of the MIM material are caused by considerable remaining porosity, enlarged grain size and increased interstitial content. Prolonged sintering times lead to improved density and strength. At the same time, the room temperature ductility is observed to drop to very low levels, presumably because of additional grain growth.     

7075铝合金化学镀对镍磷合金镀膜组织和性能的影响

金属表面处理直接影响7075铝合金的力学性能及耐腐蚀性能.以7075-T6铝合金为基体,采用化学镀(EN)技术在光滑基体表面均匀镀覆一定厚度的镍磷(Ni-P)镀膜,镀膜厚度分别为3.64、5.87和7.33 μm,并通过扫描电子显微镜(SEM)、X射线衍射(XRD)、硬度测试及电化学工作站等手段分析膜层特性及膜厚对70...