Al-Si Matrix Research Articles

Tensile fracture behavior and friction and wear properties of TiB2 particle reinforced Al-Si matrix composites

In this study, TiB2/Al-Si composite material was fabricated by addition of Al-TiB2 master alloy, and the influence of varying micro-sized TiB2 particle content on the mechanical and tribological properties of the composite material was investigated. The results revealed that the introduction of TiB2 particles effectively refined the Al-Si matrix alloy microstructure, thereby enhancing the mechanical properties and wear resistance of the Al-Si matrix alloy. When the TiB2 particle content reached 0.8 wt%, the composite material exhibited optimal mechanical properties with a tensile strength of 318 MPa and elongation of 7.2 %, improving of 8.9 % and 69.1 %, respectively, compared to the matrix alloy. Moreover, wear rates of the composite material demonstrated significantly lower than the matrix alloy under different loading conditions in this paper. The improved mechanical properties of the composite material were attributed to grain refinement strengthening, second phase strengthening and the coefficient of thermal expansion strengthening. Under low loads, abrasive wear was the dominant wear mechanism; while under high loads, a combination of abrasive and adhesive wear occurred. The addition of TiB2 particles effectively enhanced the hardness of the matrix alloy, reduced the dynamic friction coefficient, suppressed adhesive wear, and improved the wear resistance of the composite material.

Dynamic ablation of C/C-SiC-AlSi and C/C-SiC-ZrB2-AlSi at changing impacted angle

Thermal protection component and jet vane of aircraft with trajectory transfer ability are attacked by heat flow from variable direction. To understand the dynamic ablation characteristics, C/C-SiC-AlSi and C/C-SiC-ZrB2-AlSi were ablated in plasma at cyclic changing impacted angle (±45o) and compared with the conventional test at steady state. Accompanied with higher and fluctuant surface temperatures, the periodical changed stress from scouring accelerated the consumption of AlSi matrix and strengthened the mechanical denudation of carbon fiber, which led to severer ablations in the dynamic environment.

Mechanical and Tribological Properties of Hybrid and Monolithic Reinforced Hypoeutectic Al–Si Matrix Composites

This study investigates the combined influence of Si element and reinforcing particles on the hardness and wear performance of aluminum matrix composites. The composites in focus include Fe‐based metallic glass (FMG) monolithic reinforced and FMG/SiC hybrid reinforced Al‐5 wt% Si matrix composites, fabricated through spark plasma sintering (SPS). A comprehensive investigation is carried out, encompassing the analysis of microstructural attributes and the examination of worn surfaces through field emission scanning electron microscopy (FESEM). Additionally, the study scrutinized two pivotal factors—hardness and density—recognizing their pivotal roles in determining the tribological performance of these composites. The experimental findings demonstrated the presence of an oxide protective layer on the worn surfaces of all specimens. Although, FMG/SiC hybrid reinforced Al‐5 wt% Si matrix composite possessed the highest hardness value, the best tribological performance is observed in Si‐bearing monolithic reinforced composite. The addition of Si to the matrix of monolithic reinforced composite facilitates improved densification behavior and enhances the distribution of reinforcing particles, resulting in a more stable and protective oxide layer in this specific sample. Furthermore, the study identifies a transition in the operative wear mechanisms from delamination to mild abrasion and adhesion with the inclusion of Si element.

Refinement of the Manufacturing Route and Evaluation of the Reinforcement Effect of MAX Phases in Al Alloy Matrix Composite Materials

Microwave Assisted Self-propagating High-temperature Synthesis (MASHS) was used to prepare open-porous MAX phase preforms in Ti-Al-C and Ti-Si-C systems, which were further used as reinforcements for Al-Si matrix composite materials. The pretreatment of substrates was investigated to obtain open-porous cellular structures. Squeeze casting infiltration was chosen to be implemented as a method of composites manufacturing. Process parameters were adjusted in order to avoid oxidation during infiltration and to ensure the proper filling. Obtained materials were reproducible, well saturated and dense, without significant residual porosity or undesired interactions between the constituents. Based on this and the previous work of the authors, the reinforcement effect was characterized and compared for both systems. For the Al-Si+Ti-Al-C composite, an approx. 4-fold increase in hardness and instrumental Young's modulus was observed in relation to the matrix material. Compared to the matrix, Al-Si+Ti-Si-C composite improved more than 5-fold in hardness and almost 6-fold in Young's modulus. Wear resistance (established for different loads: 0.1, 0.2 and 0.5 MPa) for Al-Si+Ti-Al-C was two times higher than for the sole matrix, while for Al-Si+Ti-Si-C the improvement was up to 32%. Both composite materials exhibited approximately two times lower thermal expansion coefficients than the matrix, resulting in enhanced dimensional stability.

Regulating the microstructure of Ti@TiAlSi core-shell structured reinforcing particles endows Al–Si alloy matrix composites with high strength and ductility

Forming spherical core-shell (CS) structured reinforcing particles, consisting of a Ti core and a surrounding TiAlSi intermetallic shell, by in situ reaction between Ti and Al matrix is a promising approach to overcome the strength-ductility trade-off in particle reinforced Al–Si matrix composites. However, the phase constituent and microstructure of the shells are highly sensitive to the Al–Si alloy composition and processing parameters of the powder thixoforming method. Therefore, the effects of Si content and partial remelting temperature on the microstructure of CS particles and the tensile properties of the resultant composites were investigated in this study. The results indicate that uniform and compact shell can be achieved only by the τ2-phase reaction layer generated during partial remelting. To form the τ2 phase, the Si content in the liquid phase of the semisolid billet prior to thixoforming must be higher than 10.3 wt%. This can be achieved through adjusting the Si content in the Al–Si alloy matrix or/and partial remelting temperature. Moreover, the Ti core radius to shell thickness ratio of ∼1.5 was proposed to achieve the composites with both high strength and ductility. These findings are helpful for designing the microstructure and fabricating CS particles reinforced metal matrix composites with excellent comprehensive mechanical properties.

Pore Structure and Deformation Correlation of an Aluminum Foam Sandwich Subject to Three-Point Bending.

An Al-Si matrix foam sandwich (AFS) with 6063 Al alloy cover sheets was fabricated by hot rolling combined with melt foaming. A foamable AlSiMg1/SiCp matrix precursor was prepared by the melting route. Hot rolling at 480 °C was carried out to obtain a mechanical bonding interface between the cover sheet and the foamable precursor. Meanwhile, the pore structure of the AFS was deeply affected by the foaming temperature and foaming time during the foaming process. Different pore growth mechanics of the crack-like pore disappearance mechanism (CDM) and pore active expansion mechanism (AEM) were concluded based on the pressure difference in pores inside and outside. Three bending tests were applied to three types of AFSs with different pore structures to evaluate the relation between pore structures and AFS mechanical properties. The bending property of the AFS with fewer layers of pores is like that of a dense material. The bending property of the AFS with a pore size in the range of 0~1 mm presents a typical sandwich shear failure mode. The AFS with a uniform pore structure, in which the shapes of the pores are predominately polygons and the pore diameter is concentrated in the range of 0.5~3 mm, processes a good energy absorption capacity, and the bending stress-strain curve fluctuates greatly after the first stress drop.

Experimental and optimization of die casting parameters on Al-Si alloy with snail shell reinforcing agent

The demand for aluminum in various fields continuously grows, including in the automotive industry. In this industry, aluminum is used as the material for the spare part. Therefore, aluminum with high mechanical properties and low casting defects is required. One of the available alternatives for producing excellent aluminum is through aluminum casting, including die casting. Die casting offers low cost in mass manufacturing of complex shaped components with acceptable casting results. Further, the selection of die-casting parameters and the addition of reinforcing elements can also improve the mechanical properties of aluminum. In this study, we strengthened the Al-Si matrix using High Pressure Die Casting process with particles from snail shell powder (calcium carbonate). Further, this study also explores the mechanical properties and microstructure of the product produced through experiment and optimization. The optimization was adopted to identify the optimum parameter. For the optimization, we used the Taguchi method. Our analysis results suggested that the reinforcing agent from the snail shell powder has the CaO and Ca(OH)2 phases, with a crystallite size of 106.59 nm. The morphology of the shell powder reinforcing agent showed the presence of agglomeration and interconnected structures, such as skeletons, with average particle size of 0.4 micro. The functional group of the shell powder reinforcing agent showed the OH band during the water absorption by CaO, along with asymmetric C–O with vibration from the carbonate group and Ca–O bound. The most excellent hardness level was identified from T8, with 86.33 HRB and die casting parameters of 0.15% reinforce agents, 750 °C temperature injection, and 50 MPa pressure. Meanwhile, the best tensile strength was found from the T9 sample, with 109,95 MPa and die casting parameters of 0.15% reinforce agents, 800 °C temperature injection, and 60 MPa pressure. Microstructure on the used piston die casting sample with snail shell powder reinforcing agent showed the presence of Al, Si, dendrite, and Al4Ca phases. The multiple response analysis on the three factors indicated that the reinforcing agent presented the most significant effects toward the tensile strength and hardness, followed by pressure and temperature injection. Meanwhile, the Taguchi method and ANOVA results showed the optimal parameter die casting was obtained from a combination of 0.15 wt% reinforce agent, 800 °C injection temperature, and 50 MPa pressure. A multiple linear regression mathematical model for tensile strength and hardness was developed from the observed data. In regression model, the value of R2 of tensile strength 74.02% and R2 of the hardness is 95,18% Thus, the developed model can be effectively used to predict the tensile strength and hardness

Irradiation performance of a U-7Mo in Al-Si matrix dispersion full-size fuel plate assembly

The Korea Atomic Energy Research Institute (KAERI) is leading the Ki-Jang Research Reactor (KJRR) project with the intent to develop a new reactor for medical isotope production and other nuclear research purposes. The KJRR core is designed to use high density fuel system where uranium alloyed with 7 wt% molybdenum (U-7Mo) particles are dispersed in a matrix of aluminum alloyed with 5 wt% silicon (Al-5Si) and clad in aluminum alloy 6061 (Al-6061) to form fuel plates. KAERI developed a fabrication facility to construct KJRR fuel assemblies and partnered with the Idaho National Laboratory (INL) to irradiate a full-size fuel assembly, with 21 total fuel plates, in the Advanced Test Reactor (ATR). Irradiation testing and subsequent Post Irradiation Exam (PIE) campaigns were performed successfully over a multi-year project. Monte Carlo neutronic calculations, coupling with a depletion code, were performed based on ATR’s as-run power history which showed that the highest power plate (plate 20) reached 83.1 % end-of-life (EOL) local burnup based on initial 235U content. Finite element thermal modeling was performed based as-run power history which showed a beginning-of-life (BOL) peak local heat flux of 184 W/cm2. No anomalous fuel performance was observed during the irradiation and target test conditions were achieved. PIE showed favorable performance of the fuel assembly regarding all important phenomena. This paper describes the KJRR fuel assembly irradiation conditions and PIE data to support the conclusion that it performed well, without evidence of unexpected or problematic fuel performance, within an irradiation test designed to bound the KJRR design environment.

Wear performance of composite dual-layer coated Al-12Si alloy: Effect of Al2Ce reinforcement and micro-arc oxidation

An attempt has been made to enhance the wear resistance of Al-12Si alloy by forming a dual-layer coating consisting of an Al-12Si matrix composite layer (Al-12Si + ∼40 vol % Al2Ce) and an external composite oxide layer. While the hardness of monolithic Al-12Si alloy was ∼110 HV, the Al-12Si matrix composite layer has got hardness of ∼140 HV and exhibited ∼6 times higher sliding wear resistance due to the suppression of the plasticity-induced adhesive wear by Al2Ce particles. Applying micro-arc oxidation (MAO) as a post-treatment favoured an oxide layer (Al2O3) on the Al-12Si alloy and a composite oxide layer (CeO2 + Al2O3) on the Al-12Si matrix composite layer. The MAO coatings fabricated on the Al-12Si alloy and Al-12Si matrix composite layer, with hardness of ∼11 GPa and ∼13 GPa, respectively, provided more than two orders of magnitude increase in the wear resistance by shifting the wear mode to elasticity-dominated wear. However, the critical load imposing the complete detachment of the MAO coating by intense cracking and spallation during testing was determined as 3 N for the MAO'ed Al-12Si alloy and 5 N for the MAO'ed Al-12Si matrix composite layer. The wear resistance of the MAO coating of the Al-12Si matrix composite layer was ∼2 times higher than that of the MAO coating of the Al-12Si alloy below the critical test loads, where the coatings remain intact with the substrate.

Microstructure and tribological behavior of Al–12Si – Nano graphene composite fabricated by laser metal deposition process

To improve the wear resistance of the Al-based alloys and extend its application spectrum, graphene nano-platelets (GNPs) reinforced Al–12Si matrix composites were fabricated by laser melting deposition (LMD) technology. The microstructure, wear morphologies and surface roughness were characterized by scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) setups and 3D confocal microscopy. The microhardness and high-speed reciprocating frictional properties both Al–12Si and GNPs/Al–12Si composites were evaluated. The addition of graphene significantly refines the microstructure and improves the wear resistance of the matrix. The formation of a relatively stable mechanically mixed layer (MML) reduces the contact area between the friction pair material and the wear surface, the wear rate and roughness of the Al–12Si – 0.5 wt% GNP reinforced composites decrease with the increase of sliding speed, and the wear mechanism changes from adhesive wear accompanied by abrasive wear to fatigue wear. Meanwhile, as the load increases, the wear rate and roughness increase. The wear mechanism of the composite changes from abrasive wear to a mixed mode (combination of both adhesive and abrasive). This research not only offers valuable information about the Al–Si-based composites but provides theoretical light on their industrial applications.

Effect of Cu addition on the microstructure, thermal physical properties and cyclic ablation of C/C-AlSi composite

Al alloy modified C/C composites are one of the most promising light-weight materials. To understand the influence of alloying, AlSi and AlSiCu melts were pressure infiltrated into porous C/C skeletons respectively and the ablation properties were mainly studied. Results showed that Cu and Al generated Al2Cu in AlSi matrix, and the compression strength of the composite was enhanced while the thermal conductivity and the phase transition temperature decreased. The matrix alloy with Cu softened and melted faster and more during cyclic ablation, which protected the C/C skeleton form thermal stress damage. Thus, the addition of Cu led to a decrease in linear ablation rate.

Effects of the Si element on the microstructure and mechanical properties of an Al/FMG/SiC hybrid composite

Enhancing the mechanical properties of metal matrix composites can be achieved through the modification of the chemical composition of the matrix. However, the specific role of silicon (Si) as an important alloying element in the context of Al matrix hybrid composites simultaneously reinforced with metallic glass and ceramic particles has not been extensively studied. Therefore, this present study aimed to investigate the effects of Si element on the microstructure and mechanical properties of an Al–Si matrix composite reinforced with SiC and Fe-based metallic glass (FMG) particles. The composite was fabricated using a powder metallurgy approach. The amount of Si was selected to position the resultant alloy solidus temperature in the super-cooled liquid region of the FMG reinforcing particles. Results showed that a small amount of Si formed an Al-rich solid solution in the Al matrix, while the rest was observed as Si-rich regions in the microstructure. Adding Si to the matrix improved densification behavior and reduced porosity content during sintering, resulting in a more homogeneous distribution of reinforcing particles. The compressive yield strength and hardness of the composite with Si in its composition were 82% and 74% higher, respectively, than the same composite without Si, confirming the effectiveness of incorporating Si in the matrix.

Investigation of The Effect of Cr2O3 Particles on Al-Si Matrix Composites Produced by Powder Metallurgy

Metal matrix composite materials can be produced by powder metallurgy method. In this study, composite material with Al+12wt%Si matrix was produced by powder metallurgy (P/M) method. Al+12wt%Si powder was mixed by adding 5wt%, 10wt% and 15wt% Cr2O3 powder. Al+12wt%Si + Cr2O3 mixture powders were pressed unidirectional with 500MPa pressure in a cylindrical mold and sintered at 500 ºC. After sintering, optical microstructure, Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and microhardness analyzes of the samples were made. When the results were examined, it was observed that a porous structure was formed in all of the samples. Moreover, the lowest amount of microhardness was measured in the sample added %15wt Cr2O3 powder sintered at 500 ºC.

Mechanical and tribological behaviour of novel Al–12Si-based hybrid composites

Abstract Aluminium matrix composites with high abrasion resistance, which can adapt to high temperatures and difficult operating conditions, are needed in the automotive and aerospace industries. For this purpose, Al–12Si–TiB2–Al2O3 composites were developed with the addition of TiB2–Al2O3 ceramic reinforcements at different rates and Gr at a constant rate. High densities were achieved by using the hot pressing method with powder metallurgy. Microstructural analyzes (SEM, EDS, X-RD) of the produced samples were made. In addition, mechanical properties (hardness and three-point bending) were investigated. The best tribological features were determined with the help of Taguchi, ANOVA and the prediction model. As a result, with the addition of TiB2 and Al2O3 reinforcements to the Al–12Si matrix, significant increases in hardness occur. In the bending analysis, it was determined that the reinforcements made the hybrid composite strong up to a certain point. From a tribological point of view, the A3 hybrid composite showed the best wear performance. Test conditions were analyzed with the help of Taguchi L18 orthogonal array and analysis of variance (ANOVA). With the help of ANOVA, it was determined that the most effective factors on the response parameters were the applied load and MMC type.

Compressive behaviour of open-cell Al–Si alloy foam produced by infiltration casting

Open-cell Al–Si alloy foams with different densities were manufactured by vacuum infiltration. The foam with smaller NaCl as space holders showed a mixed scaffold structure consisting of abundant struts and cell walls. It was also found that the open-cell Al–Si alloy foam showed various defects containing micropores, microcracks and missing cell walls. The compression results indicated that the open-cell Al–Si alloy foams exhibited smoother stress–strain behaviour and higher compressive strength than that of previous studies, despite a larger number of defects in brittle Al–Si matrix. The successive occurrences of multiple deformation bands owing to the mixed structure and various defects were responsible for the smooth compression stress–strain behaviour.

A novel iterative algorithm to improve segmentations with deep convolutional neural networks trained with synthetic X-ray computed tomography data (i.S.Sy.Da.T.A)

We propose a novel iterative segmentation algorithm (i.S.Sy.Da.T.A: Iterative Segmentation Synthetic Data Training Algorithm) employing Deep Convolutional Neural Networks and synthetic training data for X-ray tomographic reconstructions of complex microstructures. In our method, we reinforce the synthetic training data with experimental XCT datasets that were automatically segmented in the previous iteration. This strategy produces better segmentations in successive iterations. We test our algorithm with experimental XCT reconstructions of a 6-phase Al-Si Matrix Composite reinforced with ceramic fibers and particles. We perform the analysis in 3D with a special network architecture that demonstrates good generalization with synthetic training data. We show that our iterative algorithm returns better segmentations compared to the standard single training approach. More specifically, phases possessing similar attenuation coefficients can be better segmented: for Al2O3 fibers, SiC particles, and Intermetallics, we see an increase of the Dice score with respect to the classic approach: from 0.49 to 0.54, from 0.66 to 0.72, and from 0.55 to 0.66 respectively. Furthermore, the overall Dice score increases from 0.77 to 0.79. The methods presented in this work are also applicable to other materials and imaging techniques.

Microstructure-property evolution of mechanically alloyed Al-20 wt% Si matrix powders and sintered composites reinforced withTiB2 particulates

Microstructural, physical and mechanical properties of Al–20 wt% Si matrix alloy powders and those reinforced with TiB2 and their sintered composites were investigated in relation to TiB2 content and mechanical alloying (MA) durations. Al–20 wt% Si matrix alloy powders and those containing 5 and 10 wt% TiB2 reinforcing particles were MA’d for 1, 2, 4, and 8 h followed by consolidation and sintering at 843 K. Si solubility in a-Al matrix increased with increasing MA duration. Increasing the TiB2 content, on the other hand, resulted in a systematic drop in Si solubility over the same MA period. Scanning electron micrographs of the sintered samples revealed sub-micron-sized, rod-shaped Si and spherical Al9Si phase particles. With increasing TiB2 content and MA durations, the microhardness of the Al20Si/TiB2 composites improved. The wear resistances of TiB2 reinforced composites better by 5 to 8 times than that of the as-blended and 1 h MA’d AlSi matrix alloy. Due to the presence of the Al3Ti intermetallic phase, sintered composite samples containing 10 wt% TiB2 particles MA'd for 8 h had the maximum hardness value and lower wear resistance values than those of the Al–20 wt% Si/5 wt% TiB2 composites.

Mechanical properties of Al-Si matrix composites synergistically reinforced by high-entropy alloy and SiC nanoparticles

To improve the mechanical strength and ductility of Al-20Si matrix composites, a novel strategy was proposed by constructing nanoparticle-rich zones (NPR) in where SiC nanoparticles were embedded into fine-grain high-entropy alloy particles (SiC@HEA). Due to the specific arrangement of SiC in HEA reinforcement, the mechanical properties of as-fabricated Al composites with hierarchical microstructure were improved significantly. The influences of hierarchical structure and interface between the NPR zones and Al matrix on tensile strength and ductility were systematically studied. The results show that the designed composite exhibits NPR zones and nanoparticle-free (NPF) zones, leading to a typical bimodal structure. The NPR zones have a higher density of geometrically necessary dislocations (GND) than NPF zones, and hence it can act as “hard” regions by enhanced dislocation strengthening and grain refinement. The large Al grains in NPF zones actet as “soft” regions to promote plastic deformation. The SiC@HEA/Al interface featured a dual-layer, including the inner layer (∼200 nm) of Ni2Si, FeNi, Ni3Si2, and FeSi phases, and the outer layer (∼300 nm) of Ni5Si2, Ni2Si, and FeNi phases. A good combination of tensile strength (251 MPa) and elongation (9%) was realized in SiC@HEA/Al composite. This study provides a new route to fabricate composites with enhanced both strength and ductility.

A literature review on Al-Si alloy matrix based in situ Al-Mg2Si FG-composites: Synthesis, microstructure features, and mechanical characteristics

The current study examined a comprehensive review of the literature on functionally graded composites, particularly Al-Mg2Si in situ metal matrix composites. Functionally graded Al-Si-Mg2Si in situ metal matrix composites are potential materials for meeting a variety of property demands in various components of automotive engines. The in situ formed intermetallic compound Mg2Si in Al-Si matrix exhibits a high melting temperature, low density, high hardness, a low thermal expansion coefficient, and a reasonably high elastic modulus. Due to all of aforementioned characteristics, Mg2Si is an attractive form of reinforcement that can be created in situ using a simple melt reaction approach. However, the coarse size of primary Mg2Si reinforcement in cast composites is a demerit which reduces the strength and ductility of the ultimate composite. Hence several researches have been attempted to refine the primary Mg2Si particles as well as to change the morphology of the eutectic structure. Apart from the monolithic in situ cast composites, attempts have been made to develop functionally graded (FG) composites in which the volume% of segregation of reinforcements are intentionally varied from one surface to another. These types of FG composites are economically developed by centrifugal casting technique in which Mg2Si reinforcements are segregated to inner the surface due to lower relative density with respect to the molten Al matrix. This type of graded microstructure results in higher strength, hardness and wears resistance at the inner surface of the tubular products. The as-cast microstructure and properties are significantly improved by solution treatment and aging. In the last, some of the most recent manufacturing techniques for FG-composites are addressed, along with their benefits, drawbacks, and applications. In general, all cutting-edge and detailed surveys of the present state of knowledge are included in this article.

Investigation on synergetic effect of non-contact ultrasonic casting and mushy state rolling on microstructure and hardness of Al–Si–Al2O3 nanocomposites

AbstractThe present work elucidates a novel way of processing Al–Si–Al2O3 bulk nanocomposites. The novel approach includes synergetic effect of non-contact ultrasonication and mushy state rolling for achieving appreciable uniformity in the distribution of nanoparticles in the metal matrix. A systematic study on the distribution of particles, the resultant microstructure, and also the resultant hardness in the nanocomposite has been presented. It is shown that the current methodology has resulted in enhanced distribution of nanoparticles in the metal matrix as compared to the earlier versions in the field. The structure of the nanocomposites has been explained on the basis of cavitation phenomena and particle pushing during solidification. The work also includes simulation using the Fluent platform to estimate the time available before the initiation of solidification to carry out effective deagglomeration and distribution of nanoparticles in the liquid melt using ultrasonic cavitation. Although the non-contact ultrasonic casting has resulted in a nearly uniform deagglomeration of nanoparticle clusters, a small number of agglomerates were present at the grain boundaries. Hence, the as-cast nanocomposites were deformed in the mushy state condition. An attempt has been made to explore the feasibility of enhancing the distribution of nanoparticles in the Al–Si matrix through semisolid state rolling. The synergetic effect has resulted in enhancement of the hardness of the material by 37%.