Nickel-based superalloys have a wide range of high-temperature applications, such as turbine blades. The complex geometries of these applications and the specific properties of the materials raise difficulties in the surface finishing. Magnetic abrasive finishing (MAF) has proven effective in finishing the complex geometries. In MAF, the magnetic properties of the workpiece, tool, and abrasive play important roles in controlling finishing characteristics. This paper presents the effects of nickel coating on the abrasive behavior during finishing and resulting finishing characteristics of Ni-based superalloys. The Ni-coated diamond abrasive is more attracted to the magnet than the Ni-based superalloy surface. As a result, fewer Ni-coated diamond abrasive particles, which are stuck between the magnetic-particle brush and the target surface, participate in surface finishing. Because of this, coupled with the reduced sharpness of abrasive cutting edges due to the coating, Ni-coated diamond abrasive cannot effectively smooth the target surface in MAF. However, the Ni coating is worn off during finishing of the hard, rough, additively manufactured surface. Then, the diamond abrasive participates in finishing as uncoated diamond abrasive and facilitates the material removal, finishing the target surface.

Nickel-Titanium (NiTi) alloy is difficult to be machined and fabricated due to its properties of rapid work-hardening and superelasticity. Traditional manufacturing methods, such as casting, vacuum arc melting, and hot-isostatic pressing, have disadvantages of high cost, time-consuming, and limitation in the complexity of parts’ fabrication. In order to reduce or solve these problems, laser additive manufacturing methods have been studied in the fabrication of NiTi alloy. Among the investigations, laser engineered net-shaping (LENS) in-situ synthesis of NiTi from blended Ni and Ti powders shows its unique advantage of cost-effectiveness and flexibility in tailoring NiTi’s phase transformation properties. In addition, it is reported that LENS in-situ synthesized NiTi parts have comparable properties with NiTi alloys fabricated from pre-alloyed powders. However, there are no existing investigations on the effects of processing parameters on the mechanical properties of the LENS in-situ fabricated NiTi parts. The processing parameters would have great influences on the properties of the LENS in-situ synthesized NiTi parts. This paper, for the first time, reports the effects of laser power, powder feeding rate, and Z increment of the deposition head on microstructure, microhardness, and Young’s modulus of the LENS in-situ synthesized NiTi parts.

As 3D Sand-Printing technology becomes more widely available to the casting market, the search for opportunities to take advantage of its freedom of design is critical for its rapid adoption by the casting community. This original research investigates casting design principles towards defect-free alloy Nickel-Aluminum Bronze (NAB). This is an alloy of interest for marine applications due to its corrosion resistance, mechanical strength and good castability. Numerical modeling of flow within a casting is examined, and rigging redesigns are proposed to improve casting quality by controlling flow behavior. It has been demonstrated that turbulence and filling velocity are determining factors that seriously impact casting performance due to the generation of casting defects. Among these are bifilm formations, gas and sand entrapment and cold shut. This work examines the effectiveness of mathematically designed rigging components in controlling mold filling and compares the results to a conventional casting rig. Design solutions are proposed using 3DSP that can be directly applied to casting operations of Nickel-Aluminum Bronze. The results from this study demonstrate the effectiveness of mathematically designed sprues to reduce filling velocity of Nickel-Aluminum Bronze. The procedure followed here can be extended to marine casting production environments. Findings from this study can be seamlessly transferred to castings of any geometry, alloy and pouring conditions.

Metal matrix nanocomposites (MMNCs) are anticipated to offer significantly better performance than existing superalloys. Nickel/alumina nanocomposite samples were fabricated with a powder metallurgy method, combining high-energy ball milling (HEBM) and spark plasma sintering (SPS). The objective of this research is to determine the effect of alumina nanoparticle fraction and HEBM parameters on the powder preparation and sintering processes, and resultant microstructure and properties. Nickel-based powders containing various fractions (1, 5 and 15 vol.%) alumina nanoparticles were prepared by HEBM. The initial particle sizes were 44 μm and 50 nm for nickel and alumina, respectively. The milling process was conducted by starting with mixing at 250 rpm for 5 min, followed by cycling operation at high and low speeds (1200 rpm for 4 min and 150 rpm for 1 min). Samples at different milling times (30, 60, 90 and 120 min) of each composition were obtained. Scanning electron microscopy (SEM) was used to evaluate the dispersion of nanoparticles in the powders at different milling times. SPS technique was used for consolidation of the prepared powders. SEM images showed that alumina nanoparticles are homogeneously dispersed in the metal matrix in the sample containing 15 vol.% alumina. Hardness measurements in cross sections of SPSed samples showed higher values for Ni/Al 2 O 3 MMNC compared to pure Ni.

Metal matrix nanocomposites (MMNCs) are anticipated to offer significantly better performance than existing superalloys for additive manufacturing (AM). However, traditional methods of preparing MMNC powder, such as high-energy ball milling, usually involve high cost and high energy consumption. This paper reports experimental results on a novel method to prepare MMNC feedstock powder. Nickel/alumina MMNC powder was successfully produced using electroless plating, containing a high fraction (66 vol. %) of alumina nanoparticles. Then, the MMNC powder was compacted into a disk shape with a hydraulic press and sintered with a tube furnace. After sintering at 1400 °C for 4 hours, the MMNC had a density of 4.16 g/cm 3 . Scanning electron microscopy observation, and X-ray diffractometry and energy-dispersive X-ray spectroscopy analysis were conducted on the sintered Ni/Al 2 O 3 disk. As the alumina nanoparticles were added to nickel, an increased microhardness of HV 0.5 189 was obtained.

Micro structure/parts during their useful life are significantly influenced by surface roughness quality. Machining of curve shapes is a necessity in micro-milling process. However, surface roughness in micro-milling curved surfaces is more complex, and few studies on the influence factors and prediction of the micro-milled curve surface roughness in micro-milling nickel-based superalloy have been done. The purpose of this paper is to study the effects of spindle speed, the radius of ball-end mill, axial cutting depth, and feed per tooth on the curved surface roughness in micro-milling Inconel 718 process based on single factor and orthogonal experiments. Utilizing the least square method, we build a surface roughness prediction model of micro-milled Inconel 718. Finally, experiments are conducted to verify the accuracy of the developed prediction model. The results indicate that the maximum relative error is 10.68%, and the mean relative error is 8.04%, which prove that the prediction model is correct. The work can provide a reference for selection of cutting parameters in micro-milling Inconel 718.

Inconel 718 (IN718) is a nickel based Ni-Cr-Fe super alloy. It has a unique set of properties such as good workability, corrosion resistance, high temperature strength, favorable weldability and excellent manufacturability. Due to its wide range of applications, IN718 is an alloy of great interest for many industries. Meanwhile, additive manufacturing assisted with laser has caught much interest from researchers and practitioners in the past three decades. In this study, IN718 alloy coupons are manufactured by selective laser melting (SLM) technique. The SLMed IN718 alloys are treated by ultrasonic nanocrystal surface modification (UNSM), and the residual stress distributions underneath the surfaces are measured. It is found that residual stress mostly tensile is induced while building the part by the SLM technique. The tensile stresses can be reduced to almost zero value by post heat treatment. Moreover, the heat treatment helps to homogenize the microstructure, and results in the increase in hardness. More importantly, it is observed that UNSM effectively induces compressive residual stresses in the as-built and heat-treated parts. The residual stresses of compressive nature in as built parts has depth of around 530 μm where as in heat treated parts has a depth of around 530μm.

The current study focuses on the process monitoring of thermal history and its significance in laser cladding technology. Thermal history of the molten pool during laser cladding was monitored using an IR-pyrometer and the molten pool life time, solidification shelf duration and cooling rates were calculated. Effect of these on three different cases was studied in brief: (a) Elemental segregation in nickel based super alloy, (b) Wettability between metal matrix and WC particles and (c) Decomposition of TiC particles in metal matrix. It was found that with slow cooling rate, formation of Laves phases in Inconel 718 became dominant which is detrimental to the mechanical properties. Also, slow cooling resulted in the decomposition of TiC particles resulting in poor wear properties of the coating. In contrast to the above two cases where slow cooling was found to be detrimental for mechanical properties of the coating, it increased wettability as well as bonding through diffusion between the WC particles and the metal matrix. Also the effect of presence of TiC and WC in metal matrix on molten pool thermal history was studied. The microstructures, elemental segregations and fractured surfaces were characterized using SEM and EDS analyses.

Graphene nanoplatelets (GNPs) have many outstanding properties, such as high mechanical strengths, light weight, and high electric conductivity. These unique properties make it an ideal reinforcement used for metal matrix composite (MMCs). In the past few years, many studies have been performed to incorporate GNPs into metal matrix and investigate the properties of obtained metal matrix composites. Meanwhile, fabrication of MMCs through laser assisted additive manufacturing (LAAM) has attracted much attention in recent years due to the advantages of low waste, high precision, short production lead time, and high workpiece complexity capability. In this study, the two attractive features are combined to produce GNPs reinforced MMC using selective laser melting (SLM) process, one of the LAAM processes. The target metal matrix material is Inconel 718, a nickel-based Ni-Cr-Fe austenitic superalloy that possesses excellent workability and mechanical performance and has wide applications in industries. Inconel 718 holds outstanding mechanical performance, corrosion, oxidation, and wear performance over a wide range of temperatures, making it an attractive superalloy used for high temperature service components. In the experiment, pure Inconel 718 and GNPs reinforced Inconel 718 composites with two levels of GNPs content (i.e., 0.25 and 1 wt.%) are obtained by SLM. Note that the SLM process, a novel powder mixture procedure is adopted to ensure the even dispersion of GNPs in the Inconel 718 powders. Room temperature tensile tests are conducted to evaluate the tensile properties. Scanning electron microscopy (SEM) observations are conducted to analyze the fracture surface of materials and to understand the reinforcing mechanism. It is found that fabrication of GNPs reinforced MMC using SLM is a viable approach. The obtained composite possesses dense microstructure and significantly enhanced tensile strength. The ultimate tensile strengths (UTS) are 997.8, 1296.3 and 1511.6 MPa, and the Young’s moduli are 475, 536, and 675 GPa, for 0 wt.% (pure Inconel 718), 0.25 wt.%, and 1 wt.% GNP additions, respectively. The bonding between GNPs and matrix material appears to be strong, and GNPs are well retained during the SLM process. The strengthening effect and mechanisms involved in the composites are discussed. Load transfer, thermal expansion coefficient mismatch, and dislocation hindering are believed to be the three main reinforcing mechanisms involved. It should be noted that more work needs to be conducted in the future to obtain more comprehensive information regarding other static and dynamic properties, and the high temperature performances of the GNP reinforced MMCs produced by SLM. Process parameter optimization should also be investigated.

The aim of this article is to investigate the effect of two different fixation hardware materials on bone remodeling after a mandibular reconstruction surgery and to restore the mandible’s function, healthy appearance, mastication, swallowing, breathing, and speech. The hypothesis is that using fixation hardware with stiffness close to that of the surrounding bone will result in a more successful healing process in the mandible bone. The finite element model includes the material properties and forces of the cancellous bone, cortical bone, ligaments, muscles, and teeth. The reconstruction surgery is modeled by including the fixation hardware and the grafted bone. In the sectioned mandible, to best mimic the geometry of the mandible, two single barrel grafts are placed at the top of each other to form a double barrel graft set. Two different materials were used as the mandibular fixation parts, stiff Ti-6Al-4V, and porous superelastic Nickel-Titanium (NiTi) alloys. A comparison of these two alloys demonstrates that using porous NiTi alloy as the fixation part results in a faster healing pace. Furthermore, the density distribution in the mandibular bone after the healing process is more similar to the normal mandible density distribution. The simulations results indicate that the porous superelastic NiTi fixation hardware transfers and distributes the existing forces on the mandible bone more favorably. The probability of stress shielding and/or stress concentration decrease. This type of fixation hardware, therefore, is more appropriate for mandible bone reconstruction surgery.

Inconel-100 (IN-100) which is a nickel-base alloy is used in metal components operate at the hot sections of gas turbines and jet engines due its excellent strength and corrosion resistance at high temperatures. This work presents investigations on the microstructural changes that occur during the machining process and specifically focuses on the effects of cutting parameters on the resultant average grain sizes of γ and γ′ phases and microhardness of the finished surfaces. Furthermore, finite element simulations have been performed to calculate the changes in grain sizes due to dynamic recrystallization by using the Johnson-Mehl-Avrami-Kolmogorov model.

In this paper, the development of a new mixture, called feedstock, based on nickel super-alloys for Metal Injection Molding (MIM) is presented. This feedstock, which will be used to obtain metallic parts for the aeronautic industry, is a mixture of the appropriate, environmentally friendly polymers and metallic powders. Many scientific problems should be taken into account. For example, it requires tight control of the process to achieve the strict chemical and physical properties, because of the application in aeronautic industry. Another difficulty is the large dimension and functional requirement of manufactured components, which subject to the high mechanical and thermal constraints. Additionally, the use of a biodegradable polymer makes the process more delicate because of its thermo-physical properties.

Despite their increasing use in leading industries, manufacture of alloys with superior mechanical properties have been a big challenge in the recent years. Researchers have been working on using assisted or augmented processes to overcome this challenge, with methods such as ultrasonically assisted, thermally assisted, vibration-assisted, magnetic field-assisted, and laser-assisted machining. Utilizing electrical assistance in manufacturing has not caught much attention due to its difficult-to-apply nature. However, it is possible to increase the ductility and machinability (through reduced flow stress) of certain metallic materials through the use of electricity. In this method, the electrical current resistively heats the material while aiding in deforming the material through the electroplastic effect. The limited amount of work in this topic is mainly focused on exploring the forming characteristics of relatively softer materials. Application of this augmentation to alloys with superior mechanical properties at elevated temperatures, on the other hand, has not been explored. This study aims to fill in that void through an investigation of applying different currents through the tool concentrated on the tool-workpiece contact zone. Both the titanium alloy Ti-6Al-4V and the nickel-based superalloy IN-738 were investigated, and the results showed that for both materials, there are two separate thresholds that need to be considered in any analysis. The first threshold is where the material starts to get deformed, below which no significant divergence from the baseline (no current) tests was observed. After exceeding this value, machining forces start decreasing with increasing current up to a certain point (second threshold) where the effect of electric current is reversed. If the second threshold is surpassed, the machining forces increase rapidly. Findings of this study can be used in assisting the machining of such materials.

The U.S. Department of Energy has estimated that the opportunities for industrial waste heat recuperation far exceed the current installed base of renewable energy. Of greatest potential are high temperature applications of waste heat recovery including opportunities in emerging technologies such as solid oxide fuel cells and the solar thermal processing of fuels. High temperature recuperators are typically produced from nickel super-alloys. To improve the economics of high temperature recuperation, microchannels have been applied to reduce the size and weight of the recuperators. Machining of microchannel features into these alloys is not only difficult, but expensive due to low material utilizations. Efforts to form microchannel geometries require the use of highly porous, micro-scale pyramidal truss networks inserted into low pressure microchannel to resist fin deflection. Challenges include the formability of the superalloy and the need for precision registration to the dies. In this paper, we discuss the limitations of conventional drawing for producing a truss network made from a nickel superalloy.

This paper is concerned with the reliable calibration of the grinding power model. The power model used in the present paper is expressed by formulae with grinding parameters as input arguments, and a number of model constants representing a given wheel, workpiece, and grinding fluid combination. The model constants are calibrated using measured grinding forces and power, taking into consideration of the chip formation, sliding, and plowing components of the power. These correspond to the constants of specific chip formation energy u ch , the coefficient of friction μ and average contact pressure p a , and the plowing force per unit width F ′ pl , respectively. A new generalized experimental approach was developed in this study to reflect the physical meaning of the model. Compared with other approaches, this approach does not require a pre-knowledge of the wheel wear flat area value and the regime of the average contact pressure. The proposed approach includes measurements of forces and power from surface grinding tests with a fixed set of grinding parameters conducted at different wheel dullness levels for calibrating the constant μ , as well as tests with variable workspeeds at each of the wheel dullness level for calibrating the other constants. As an application example, it was applied to calibrating the power model for grinding of a nickel-based alloy with oil as grinding fluid and electroplated CBN wheels. The calibrated model was then validated through tests under different grinding conditions.

Direct Metal Laser Sintering (DMLS) is an additive manufacturing technology that can construct medium to small size parts very efficiently in comparison to traditional machining processes. The ability of this technology to grow complex parts made of high strength titanium- and nickel-based alloys led to increasing interest from aerospace, defense, and medical industries. Although the technology allows growing parts close to their final shape, the active surfaces still need a finishing operation such as grinding to meet the tight tolerances and surface finish requirements. Due to the novelty of the DMLS technology, and the relatively recent developments of titanium alloy powders, there is a need for testing and validating the capabilities of the components manufactured through a combination of DMLS and grinding processes. This paper presents the findings of an experimental study focused on the effect of various grinding conditions on the surface integrity of titanium alloy (Ti-6Al-4V) specimens produced using DMLS technology. The goal is to identify dressing and grinding conditions that would result in ground surfaces free of defects such as micro-cracks, discoloration of surfaces and/or burn marks due to high heat generated during grinding. The residual stresses were used to quantify the effect of the grinding conditions on the ground surfaces. These investigations were conducted on an instrumented CNC surface grinding machine, using a silicon-carbide grinding wheel and a water-based fluid. The X-ray diffraction method was used to measure the residual stresses. Two batches of specimens were manufactured for these tests. The growing strategy of the specimens and the presence of apparent defects in material structure are considered some of the main causes for the differences observed in the outcomes of the grinding trials. The results of these investigations support the need for continuing research in the additive manufacturing field to develop methods and technologies that will ensure a high level of consistency of the grown parts.

Nickel-based superalloys are designed for use in extreme environments and are getting progressively better for these environments, therefore much harder to machine. They play a crucial role in elevated temperature applications where high strength, high resistance to corrosion and creep resistance are required. Machinability suffers as a result of these properties and harsh machining conditions occur, resulting in high cutting forces and tool wear. To combat the difficulties in the machining of nickel-based superalloys, such as poor thermal diffusivity and high levels of abrasive wear, trochoidal milling was introduced as an alternative method of milling. This method of milling combines linear motion with uniform circular motion, reducing chip load in exchange for increased machining time. Industry is averse to its widespread adoption due to increasing cycle times when compared to conventional milling methods, however it has been shown that overall productivity can be improved due to less tool wear with a more predictable behavior. This work characterizes the effects of trochoidal milling and provides a comparison of trochoidal milling with a traditional milling technique, end milling, for the machining of Inconel 738. In order to compare the trochoidal and conventional machining approaches directly, metrics of productivity normalized to tool wear are introduced. The normalized metrics introduced in this study aim to provide a more representative comparison of productivity and efficiency characteristics: volumetric material removal per unit tool wear ( MR/VB ) and the material removal rate per unit tool wear ( MRR/VB ). It was found that significantly higher volumetric material removal is possible using trochoidal milling, and fewer tools are needed; material removal rates that competitive with end milling can be achieved. When the amount of time spent on tool change for the same volume of material removal is considered, material removal rate of trochoidal milling can even be higher than end milling, indicating that better productivity and efficiency of the process is possible at reduced tooling costs.

Presently surface micro-texturing has found many promising applications in the fields of tribology, bio-medical engineering, metal cutting, and other functional or topographical surfaces. Most of these applications are material-specific, which necessitates the need for a texturing and machining process that surpasses the limitations posed by a certain class of materials that are difficult to process by laser ablation, owing to their optical or other surface or bulk characteristics. Laser Induced Plasma Micromachining (LIPMM) has emerged as a promising alternative to direct laser ablation for micro-machining and micro-texturing, which offers superior machining characteristics while preserving the resolution, accuracy and tool-less nature of laser ablation. This study is aimed at understanding the capability of LIPMM process to address some of the issues faced by pulsed laser ablation in material processing. This paper experimentally demonstrates machining of optically transmissive, reflective and rough surface materials using LIPMM. Apart from this, the study includes machining of conventional metals (Nickel and Titanium) and polymer (Polyimide), to demonstrate higher obtainable depth and reduced heat affected distortion around micro-features machined by LIPMM, as compared to laser ablation.

This paper presents fabrication of tapered, high aspect ratio bio mimetic cilia from Nickel-polydimethyl siloxane (Ni-PDMS) composite by using bulk lithography technique and ceramic molding. Many research groups suggested fabrication of bio mimetic cilia using various techniques which are based on soft lithography and VLSI techniques. Recently a novel single layer micro fabrication technique known as ‘bulk lithography’ which uses an unconstrained photopolymer has been reported by co-authors. This technique is used to fabricate a polymer cilia pattern (an array of photopolymerised inverted cone profile) and using this pattern a ceramic green body is fabricated by slip casting technique. An aqueous suspension containing sub micron size alumina is used to cast ceramic green body. After casting this cilia pattern makes negative impression of tapered holes on green ceramic body. During sintering of green ceramic body the polymer burns off resulting in ceramic mould with tapered holes imprinted on it. This mold retains shape of a tapered hole though it shrinks in size after sintering. This mold is used further to cast Ni-PDMS composite in the form of cilia structures.

The wear rate of a grinding wheel directly affects the workpiece surface integrity and tolerances. This paper summarizes a combined experimental-modeling framework for life cycle prediction of an electroplated Cubic Boron Nitride (CBN) grinding wheel, typically utilized in nickel-based superalloy grinding. The paper presents an experimental framework to facilitate the formulation of a micro-mechanics based modeling framework. The presented work investigates the topological evolution of the grinding wheel surface and mechanisms of grit failure via depth profiling, digital microscopy and scanning electron microscopy. The results are used to elucidate the statistical evolution of the grinding wheel surface. Different modes of grit failure, including grit attritious wear, fracture and pull out haven been identified. The analysis of the surface topological features indicates a unique grit activation process, leading to a non-uniform spatial distribution of the grit wear. Additionally, single grit pull out experiment has been conducted to assess the residual strength of the grit-wheel interface and the associated state of damage percolation. The experimental results can be utilized in developing a life expectancy model for the CBN grinding wheel to assess the grit mean time to failure as well as grit surface topological evolution as a function of the process parameters.