Design and development of ceramic-based composites with tailored properties for cutting tool inserts

In this study, the microstructural evolution and phase transformations of gas atomized Al-Cr-Fe powders during annealing process, spark plasma sintering (SPS) of Al-Cr-Fe powders and SPS of Ti/Al-Cr-Fe metal matrix composites (MMCs) were investigated. There are four phases identified in the annealed Al-Cr-Fe powders: icosahedral Al-Cr-Fe, decagonal Al-Cr-Fe, Al9(Cr,Fe)4 and Al8(Cr,Fe)5, with decagonal Al-Cr-Fe forming in the annealing process. Icosahedral Al-Cr-Fe is face-centered. Decagonal Al-Cr-Fe has a periodicity of about 1.2 nm along its periodic axis and it can be well superimposed by Penrose tilings. Al-Cr-Fe powders have been successfully sintered using SPS. With the rise of the sintering temperature from 650 ˚C to 800 ˚C, the relative density of the pellets increases from 70% to 99% and their microhardness increases from Hv 400 to Hv 810. The dominant densification mechanism of Al-Cr-Fe powders in the SPS process is powder rearrangement and dislocation motion. The SPS process promotes the formation of decagonal Al-Cr-Fe. Ti/Al-Cr-Fe MMCs with Ti as matrix and Al-Cr-Fe quasicrystals as reinforcements have been successfully prepared using high pressure SPS. Interfacial layer forms between Ti and Al-Cr-Fe during the sintering process. This layer mainly consists of Al3Ti and AlTi. With the increase of sintering pressure from 50 MPa to 300 MPa, the compositional changes of Al-Cr-Fe are reduced. The addition of Al-Cr-Fe particles to Ti matrix significantly improves the hardness and reduces the wear rate. This study shows for the first time that Al-Cr-Fe quasicrystals can be sintered using SPS and SPS process can promote the formation of decagonal Al-Cr-Fe and the increased sintering pressure leads to reduced compositional changes of Al-Cr-Fe reinforcements in the Ti based MMCs prepared using SPS.

Gas-atomized Ni52:5Nb10Zr15Ti15Pt7:5 metallic glassy alloy powders were consolidated by a spark plasma sintering (SPS) process. The densification behavior during the SPS process as well as the structure, thermal stability and mechanical properties of the sintered specimens were investigated. The glassy alloy powders were densified rapidly when the temperature exceeded about 740 K. The density of the sintered specimens increased with an increase in sintering temperature. The specimens with full densification and no crystallization were obtained by the SPS process at a sintering temperature of 773 K with a loading pressure of 600 MPa. The sintered specimens exhibit high-strength and can meet large-size requirement. [doi:10.2320/matertrans.ME200817]

Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Cocaine is recognized as the most reinforcing of all drugs of abuse. There is no anticocaine medication available. The disastrous medical and social consequences of cocaine addiction have made the development of an anticocaine medication a high priority. It has been recognized that an ideal anticocaine medication is one that accelerates cocaine metabolism producing biologically inactive metabolites via a route similar to the primary cocaine-metabolizing pathway, i.e., cocaine hydrolysis catalyzed by plasma enzyme butyrylcholinesterase (BChE). However, wild-type BChE has a low catalytic efficiency against the abused cocaine. Design of a high-activity enzyme mutant is extremely challenging, particularly when the chemical reaction process is rate-determining for the enzymatic reaction. Here we report the design and discovery of a high-activity mutant of human BChE by using a novel, systematic computational design approach based on transition-state simulations and activation energy calculations. The novel computational design approach has led to discovery of the most efficient cocaine hydrolase, i.e., a human BChE mutant with an approximately 2000-fold improved catalytic efficiency, promising for therapeutic treatment of cocaine overdose and addiction as an exogenous enzyme in human. The encouraging discovery resulted from the computational design not only provides a promising anticocaine medication but also demonstrates that the novel, generally applicable computational design approach is promising for rational enzyme redesign and drug discovery.

Microstructure and transformation of Al-containing nanostructured 316L stainless steel coatings processed using spark plasma sintering

Graphite-molybdenum-titanium composites might attract significant interest as heat sinks for different sector applications due to their excellent thermal, electrical and mechanical properties. This type of composites was already studied but following the powder metallurgy and spark plasma sintering (SPS) route. The aim of the present investigation is to study a new route of fabrication of these composites to improve their properties: colloidal synthesis and SPS process. The results obtained for graphite-10 vol% Mo-1 vol% Ti composites prepared by both routes are compared. It has been proved that the properties of the composites are significantly improved by the colloidal route compared with the powder metallurgy route, i. e. electrical conductivity by a factor of 3, thermal properties by a factor of 8 and bending strength by a factor of 4.

Hybrid metal matrix composite constitutes a tough metal matrix with reinforcement of at least two ceramic particulates and exhibit superior mechanical and thermal properties. The difficulties in machining metal matrix composites are obtaining good surface finish, consumption of more electrical power, involving excessive cutting forces and greater tool wear as it contain very hard ceramic particulates. This factor restrict the wide spread application of these kind of materials. Hence the study of machining characteristics and the optimization of the cutting parameters are prime importance. In this paper aluminium alloy is taken as metal matrix and the silicon carbide (SiC 10% by wt.) and boron carbide (B4C 5% by wt.) taken as ceramic reinforcement. This material is fabricated in the form of cylindrical rod using stir casting method. Turning operations are carried out in medium duty lathe using poly crystalline diamond (PCD) cutting tool insert. Taguchis design of L09 orthogonal array is followed selecting three machining factors namely cutting speed, feed and depth of cut at three levels. Optimal cutting conditions are arrived by Signal-Noise ratio method with respect to surface roughness. The results are validated by (ANOVA) analysis of variance and the percentage of contribution of cutting speed, feed rate and depth of cut for better surface finish are determined and it is found that the vital parameter is feed followed by cutting speed and then by depth of cut.

Spark plasma sintering versus hot pressing – densification, bending strength, microstructure, and tribological properties of Ti5Al2.5Fe alloys

In this study, the effect of single and hybrid nanofillers on the thermal, mechanical, and physical properties of polypropylene composites were carried out. This nanocomposite was compounded using two-roll mill mixing method and the filler content was fixed at 4 vol % loading. The single filler used is synthetic diamond (SD), boron nitride (BN), and carbon nanotube (MWNT). The hybrid system was composed by addition of MWNT into single SD and BN. The prepared samples were characterized by thermal properties, tensile and flexural, and these results were supported by the morphology, void content, and melt flow index values. The result showed that the hybrid composite with combination of BN and SD with MWNT indicate higher thermal conductivity and thermal stability and lower thermal expansion. However, no significant improvements in tensile and flexural strengths were observed due to large formation of agglomeration as being captured by SEM micrographs. Furthermore, the existence of higher percent void content suggests low adhesion and poor compatibility between hybrid filler and matrix. This caused detrimental effect of strength of hybrid composites rather than single filler composites.

High-strength aluminum-based composites reinforced with BN, AlB2 and AlN particles fabricated via reactive spark plasma sintering of Al-BN powder mixtures

Over the past two decades, colloidal particles with a variety of shapes, sizes, and compositions have been synthesized and characterized successfully. One of the most important applications for colloidal building blocks is to engineer functional structures as mechanical, electrical, and optical metamaterials. However, complex interaction dynamics between the building blocks as well as sophisticated structure-property relationships make it challenging to design structures with predictable target properties. In this paper, we implement an inverse material design framework using Genetic Algorithm (GA)-based techniques to streamline the design of colloidal structures based on target properties. We investigate spherical particles as well as colloidal molecules of different sizes and shapes and evaluate a Geometric Landscape Accessibility parameter that identifies the size of feasible domains within the geometric phase space of each structure. Considering target photonic properties, our GA-assisted framework is further utilized to identify sets of building blocks and structures that lead to various target values for the size of the photonic band gaps. The proposed framework in this study will provide new insight for predictive computational material design approaches and help establish more efficient ways of understanding structure-property relations in sub-micrometer-scale materials.

Alumina materials are widely used in the industry as cutting tool inserts. In order to improve mechanical properties of the Al2O3 matrix, different reinforcing phases are introduced. In the presented work, reinforcements in the form of ZrO2 particles and SiC nanofibres have been used. ZTA-SiC composites were obtained from 0.5%MgO-20%(3Y2O3)ZrO2-79.5%Al2O3 powder and 15% of SiC whiskers. Tested materials have been prepared by means of the two-step sintering (TSS) and spark plasma sintering (SPS). TSS method permits to obtain dense materials with fine-grained microstructure. TSS has been carried out for two different sintering times: 1 hour 20 minutes and 8 hours. Due to the reactivity of the components, the SPS method has been used to shorten sintering times. SPS has been performed at two different temperatures: 1500 °C and 1550 °C.

Anti-ferroelectric (AFE) composite ceramics of (Pb0.858Ba0.1La0.02Y0.008)(Zr0.65Sn0.3Ti0.05)O3-(Pb0.97La0.02)(Zr0.9Sn0.05Ti0.05)O3 (PBLYZST-PLZST) were fabricated by the conventional solid-state sintering process (CS), the glass-aided sintering (GAS), and the spark plasma sintering (SPS), respectively. The influence of the temperature induced phase transition on the phase structure, hysteresis loops, and energy storage properties of the composite ceramics were investigated in detail. The measured results of X-ray diffraction demonstrate that the composite ceramics exhibit the perovskite phases and small amounts of non-functional pyrochlore phases. Compared with the CS process, the GAS and SPS processes are proven more helpful to suppress the diffusion behaviors between the PBLYZST and PLZST phases according to the field emission scanning electron microscopy, thereby being able to improve the contribution of PBLYZST phase to the temperature stability of the orthogonal AFE phase. When the ambient temperature rises from 25 °C to 125 °C, CS and GAS samples have undergone a phase transition from orthorhombic AFE phase to tetragonal AFE phase, which results in a sharp decline in the energy storage density. However, the phase transition temperature of SPS samples is higher than 125 °C, and the energy storage density only slightly decreases due to the disorder of material microstructure caused by the high temperature. As a result, the SPS composite ceramics obtain a recoverable high energy storage density of 6.46 J/cm3 and the excellent temperature stability of the energy storage density of 1.16 × 10−2 J/°C·cm3, which is 1.29 × 10−2 J/°C·cm3 lower than that of CS samples and about 0.43 times as that of GAS samples.

Cellulose and silk blended biomaterial films were regenerated from ionic liquid solution and investigated to characterize and understand the effect of inter- and intra-molecular interactions upon the morphology and thermal properties. The blended films were dissolved in 1-allyl-3-methylimidazolium chloride ionic liquid, coagulated and regenerated with water. Various characterization techniques were implemented to characterize structural, morphological and thermal properties: FTIR, SEM, TGA, DSC and X-ray scattering. The results showed that the cellulose microcrystalline structure and β-sheets from the silk can be disrupted by inter- and intra-molecular hydrogen bonds forming intermediate semicrystalline or amorphous structures. The SEM showed morphological effects of such interactions that cause varying thermal degradation and glass transition temperature. The X-ray scattering confirms such findings at the molecular level, demonstrating that the cellulose microfibril diameter decreases as the silk content increases. It also shows that the β-sheets size increases as the cellulose content increases. These various techniques provide evidence that suggest the hydrogen bonds between the β-sheets and the glucose units in the cellulose chains control the thermal and structural properties of the blended films, changing the morphology and physicochemical properties.

Nickel foam of various pore-size coated graphene thin film of 200 nm thickness was investigated as a function of the pore size. The structural properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The optical properties were analyzed through the UV–Visible reflectance and Photoluminescence spectra. Hall Effect and Electrochemical impedance spectroscopy techniques were used to study the electrical and dielectric properties. The thermal properties were measured through the photothermal deflection technique. By decreasing the pore size, the electrical conductivity was increased from 9.42 × 107 to 33.26 × 107 S m−1, volume and surface carrier densities were decreased from −8.66 × 1021 to −2.05 × 1021 cm−3 and from −1.13 × 1014 cm−2 to −0.41 × 1014 cm−2; respectively, the specific capacitance was increased from 15.52 × 106 F to 19.65 × 106 F and the dielectric permittivity of value in the order of 1.5 × 103 F m−1 was decreased with the frequency. It was developed the photothermal deflection technique and discussed its sensitivity to the determination of thermal properties which show that the thermal conductivity decreased from 4.12 to 3.58 W m−1 K−1 and the thermal diffusivity decreased from 0.146 to 0.109 cm2 s−1. It was established semi-empirical relationships which allow to deduce the thermal properties and optical band gap without needing to measure them. These results introduce the graphene coated on Nickel foam sheets as good candidate for potential use in photoelectric and thermoelectric devices.