Ductile Matrix Research Articles

Grinding of steel-ceramic-composites

Steel-ceramic composites offer a high potential as protective layers of mechanically and abrasively highly loaded parts. However, the machining of steel-ceramic composites is a great challenge for the process design due to the very different mechanical properties of the brittle ceramic particles embedded in the ductile steel matrix. Both materials must be machined simultaneously in a ductile mode to gain high surface qualities. This paper introduces a new process characteristic that describes the influence of the peripheral grinding process settings and tool specifications on the process forces and workpiece surface roughness when grinding steel-ceramic composites. An empirical model is derived to estimate the surface roughness depending on the process settings and tool specifications. It is also shown that the results gained in peripheral grinding can be transferred to face grinding. Adequate process parameters can be therefore estimated in both grinding processes to gain high surface qualities.

AlSi11/ Si<sub>3</sub>N<sub>4</sub> Interpenetrating Composites Tribology Properties of Aluminum Matris Composites

In present work, the metal-ceramic interpenetrating composites (IPCs) as AlSi11/ Si3N4 are fabricated by infiltrating technique. IPCs exhibit special characterization of brittle ceramic reinforced phase introduced by ductile metal matrix phase. During the sliding wear processes, IPCs exhibit four wear mechanism such as initial adhesive wear, mixed adhesive and abrasive wear, adhesive wear and final abrasive wear. Reinforcements inhibit plastic flow and restrict propagation of wear cracks. Increase in the volume fraction of reinforcement leads to improvement in the wear resistance. Under higher load and lower round speed conditions, the friction coefficients are lower than that of relative conditions.

Effects of the microstructure and minor elements on the fracture toughness of Nb-Si alloy

ABSTRACTThe development of a new high temperature structural material is recently required in various fields. As one of the potential materials, Nb-Si alloys have attracted attention due to their high melting point and low density. A microstructure composed of ductile Nb matrix containing finely dispersed spherical Nb5Si3 phase is obtained by the addition of ternary elements such as Au and it is found that such microstructure is effective in improving room temperature toughness. The main purpose of the present study is evaluating fracture toughness of Nb-Si-Au alloys using small specimens and investigating the effects of the microstructure and other minor elements on the fracture toughness. Alloy ingots of Nb-15at.%Si-3at.%Au and Nb-3at.%Au are prepared by arc-melting under Ar atmosphere, followed by heat-treatments at up to 1500oC for 100 hours. Chevron notched specimens with a size of 1.0x2.0x10mm are subjected to four-point bending tests under a laser confocal microscope for in-situ observation of crack propagation, and the effect of the microstructure and minor elements such as oxygen on the evaluated fracture toughness is investigated on both the Nb/Nb5Si3 alloys and the Nb solid solution (Nbss) alloys.

Effects of bone particle on the properties and microstructure of polypropylene/bone ash particulate composites

The effects of uncarbonized (fresh) and carbonized bone particles on the microstructure and properties of polypropylene composites have been studied. The addition of the bone particles ranges from 5 to 25wt% in uncarbonized and carbonized forms in the polypropylene matrix. The physical and mechanical properties were used as criteria for the evaluation of the composites. Microstructures of the composites were assessed with scanning electron microscopy (SEM/EDS). The results revealed that the addition of carbonized bone particles reinforcement has superior properties than uncarbonized bone particles composite based materials with an increase in the compressive strength, hardness values, tensile strength and flexural strength by 53%, 45% and 35% respectively, and a decrease in the % elongation and impact energy by 75% and 32%, respectively at 25wt% carbonized bone, with 28% increase in tensile strength at 15wt% carbonized bone addition. The increase in strength and hardness values was attributed to the distribution of hard phases of bone particles in the ductile polypropylene matrix.

Process Parameter Impact on Microstructure of Laser Clad Inconel-Chromium Carbide Layers

Chromium carbide based metal matrix composite (MMC) coatings are ideally suited for high temperature erosive-corrosive applications. Laser cladding of such MMCs, with Inconel as the ductile matrix instead of the usual NiCr alloy, has been attempted in the present study. The relative hardness of the laser clad layers was observed to drop with increase in laser power. The reduction in hardness was attributed to retention of lower amounts of chromium carbides in the clad layer at higher laser powers. Use of chemically assisted scans with electron diffraction allowed extraction of effective micro-textural information on the coatings

Influence of silicon carbide particulates on tensile fracture behavior of an aluminum alloy

Abstract In this research paper the tensile properties and fracture characteristics of an Al–Cu–Mg alloy discontinuously reinforced with silicon carbide particulates (SiC p ) are presented and discussed. The increased strength of the Al–Cu–Mg/SiC p composite is attributed to the synergistic influences of residual stresses arising from intrinsic differences in response of the composite constituents, that is, metal matrix and ceramic-particle reinforcements, during cyclic deformation and strengthening from constrained plastic flow and triaxiality in the ductile aluminum alloy metal matrix due to the presence of ceramic particle reinforcements. Fracture on a microscopic scale comprised of cracking of both the individual silicon carbide particulates and even the clusters of silicon carbide particles present in the microstructure. Final fracture of the composite resulted from crack propagation through the matrix between the clusters of reinforcing SiC particles. The key mechanisms governing the tensile fracture process are discussed.

Oxidation resistant Mo-Mo2B-silica and Mo-Mo2B-silicate composites for high temperature applications

Development of Mo composites based on the Mo-Si-B system has been demonstrated as a possible new route to achieving a high temperature Mobased material. In this new system, the silicide phases are replaced directly with silica or other silicate materials. These composites avoid the high ductile to brittle transition temperature observed for Mo-Si-B alloys by removing the Si that exists in solid solution in Mo at equilibrium with its silicides. A variety of compositions is tested for room temperature ductility and oxidation resistance. A system based upon Mo, Mo2B, and SrO·Al2O3·(SiO2)2 is shown to possess both ductility at 80 vol.% Mo and oxidation resistance at 60 vol.%. These composites can be produced using a powder processing approach and fired to greater than 95% theoretical density with a desirable microstructure of isolated boride and silicate phases within a ductile Mo matrix.

Metallographic Study of Laser Thermal Fatigue Damage on Piston

The experiments of thermal fatigue damage on piston were conducted by shaped high power laser. Microstructure of thermal fatigue damaged specimen was characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The mechanical properties of thermal fatigue specimen were evaluated by microhardness and the corresponding damaged mechanisms were discussed. The results show that cracks originated from the interface of Al-matrix and intermetallic phase due to the thermal and mechanical mismatch between the brittle components of the microstructure and the surrounding ductile matrix. Oxides of thermal fatigue crack can accelerate the damage of piston. There exists a decline tendency in the microhardness of piston at all locations after thermal fatigue tests due to the comprehensive effects of nonequilibrium distribution of temperature and cooling method.

Micromechanical analysis of strain rate-dependent deformation and failure in composite microstructures under dynamic loading conditions

This paper is intended to study the effect of microstructural morphology and loading characteristics on micromechanical stress-wave propagation leading to different damage mechanisms, energy absorption and dissipation characteristics. The composite material microstructure is represented by brittle fibers in a ductile matrix in different arrangements. The matrix material behavior is modeled using a strain-rate dependent elastic-viscoplastic constitutive model with damage evolution based on the Gurson–Tvergaard–Needleman model with a Johnson–Cook type hardening law. Damage in the fiber is modeled by an isotropic continuum damage mechanics (CDM) model. The microstructural failure modes and energy absorption and dissipation properties show strong dependence on the load types, volume fractions and microstructures, with relatively lower dependence on strain rates. The studies show that for the SiC fiber/Al7075-T6 composites, the microstructures with 15–20% unidirectional hexagonal arrangement of fibers are good designs for energy absorption and dissipation.

Reversible Magnetic Field Induced Strain in Ni2MnGa‐Polymer‐Composites

AbstractComposite materials consisting of magnetic shape memory alloy particles and a polymer matrix combine the advantages of both material classes: the high achievable magnetic field induced strain (MFIS) of 6% of Ni‐Mn‐Ga with a ductile matrix. Engineering the particle‐matrix interface as well as matching stiffness of polymer matrix is of importance for achieving high reversible MFIS to use this material as actuator or damper. We investigated those properties for Ni50.9Mn27.1Ga22.0 and Ni50.3Mn24.6Ga25.1 polymer composites. Particles were produced by gently crushing melt‐extracted and subsequently annealed fibres. At room temperature, the Ni50.9Mn27.1Ga22.0 particles exhibit a 5M martensitic structure, while the Ni50.3Mn24.6Ga25.1 particles are austenitic. These particles were embedded into the polymer, either a stiff epoxy resin or a soft polyurethane. In response to an external applied magnetic field, the particles tend to relocate within the polyurethane due to its very low Young's modulus and magnetostatic interaction between particles. Slightly stiffer polymer matrices are advantageous for achieving controllable MFIS. In Ni50.9Mn27.1Ga22.0 epoxy composites, a MFIS of 0.1% was observed and was resettable by rotating the magnetic field by 90°. Furthermore, single fibre pull‐out tests indicated significant improvements of the interfacial properties when using silane coupling agent treated fibres.

Boudinage in nature and experiment

Deformation of rocks produces structures at all scales that are in many cases periodic (folding or boudinage), with variable amplitude and wavelength. Here we focus on boudinage, a process of primordial importance for tectonics. In the present study, we carried out measurements of natural boudins and experimentally tested the effects of two variables on boudinage: layer thickness and compression rate. The models were made of a competent layer (mostly brittle, as in nature) of either elastic (soft paper) or viscoelastoplastic (clay) material embedded in a ductile matrix of linear viscous silicone putty. The competent layer lied with its greatest surface normal to the principal shortening axis and greatest length parallel to the principal stretching axis. The model was then subjected to pure shear at constant piston velocity and variable competent layer thickness (Model 1), or at different piston velocity and constant layer thickness (Model 2). The results of Model 1 show an exponential dependence of boudin width on competent layer thickness, in disagreement with data from the studied natural occurrence. This indicates that variables other than competent layer thickness are hidden in the linear relationship obtained for the natural boudinage. The results of Model 2 show that the higher the velocity the smaller the boudin width, following a power-law with exponent very similar to that of analytical predictions.The studied natural boudinage occasionally occurs in two orthogonal directions. This chocolate tablet boudinage can be the result of two successive stages of deformation: buckling followed by stretching of competent sandstone layers, or buckling followed by rotation of reverse limbs into the extensional field of simple shear.

Grinding of Steel-Ceramic-Composites

Steel-ceramic-composites offer a high potential as protective layers of mechanically and abrasively high loaded machine parts. The machining of steel-ceramic-composites is a high challenge for the process design due to the very different material properties of the brittle ceramic particles, embedded in the ductile steel matrix. Both materials have to be machined in ductile mode simultaneously to gain high surface qualities. Thus, the material separation mechanisms have to be understood for an adequate process design. In this paper, a new process characteristic is introduced that describes the influence of the grinding process settings on the process forces and workpiece surface roughness in grinding steel-ceramic-composites.

Modelling the effect of microstructural banding on the flow curve behaviour of dual-phase (DP) steels

Dual-phase steels (DP) are well suited for automotive application due to their attractive mechanical properties, such as high strength and good formability. These properties are achieved by the dispersion of hard martensite particles in the soft and ductile ferrite matrix. The current work aims to predict the mechanical properties of dual-phase steels. A microstructure based approach by means of representative volume element (RVE) was employed for this purpose. Available and novel routines were used to create the 2D RVEs from the real microstructures. Periodic and homogeneous boundary conditions were imposed. Dislocation based model was implemented to predict the flow behaviour of the single phases. Computational first order homogenization strategy was employed to obtain the true stress–true strain curves from the RVE calculations. The implementation of the periodic boundary condition results in a better agreement with the converged effective value compared to the displacement boundary condition. Equiaxed microstructures show higher strength and work hardening compared to that of the banded microstructures. In the same fraction of martensite, the yield stress of DP steels decreases by increasing the aspect ratio of martensite bands.

Influence of Secondary Precipitations in Fe-Based MMCs on High Temperature Wear Behaviour

Reinforcing a temperature resistant matrix with carbides (MMC, metal matrix composite) is expected to improve the abrasion resistance at high temperatures. Experiments show that carbides brought in during a plasma transferred arc (PTA) welding process get partly dissolved in the martensitic matrix and secondary carbide structures precipitate. Further analyses with nano-indentation and XRD show that these secondary precipitations strongly influence the properties of the originally homogeneous ductile martensitic matrix. Although hot hardness is increased, wear resistance is diminished due to changed nano-microstructural material properties.

Studies of the properties of heat treated rolled medium carbon steel

Investigations were carried out to study critically the effects of heat treatment on the properties of rolled medium carbon steel. Representative samples of as-rolled medium carbon steel were subjected to heat treatment processes which are; Quenching, Lamellae Formation and Tempering in the following order (Q + Q + L + T), (Q + L + T) and (L + T). The steel was heated to the austenizing temperature of 830 oC and water quenched. The quenched steel was subjected to lamellae formation by reheating it to the ferrite-austenite dual-phase region at a temperature of 745 oC below the effective AC3 point and then rapidly quenched in water. The lamellae formed was tempered at 480 oC to provide an alloy containing strong, tough and lath martensite in a soft and ductile ferrite matrix. Mechanical tests were carried out on the samples and the results shows that the steel developed has excellent combination of tensile strength, hardness and impact strength which is very good for structural applications. The corrosion behaviour of the samples; heat treated rolled medium carbon steel and as-rolled medium carbon steel in sodium chloride medium were also investigated from where it was also confirmed that improved corrosion resistance is achievable by the treatment.

Mechanical Behavior of SiC Fiber Reinforced Al Matrix Composites: A Study Based on Finite Element Method

The effects of SiC fiber shape, aspect ratio and loading direction on the deformation behavior of SiC fiber reinforced Al matrix composites were studied by finite element method using axisymmetric unit cell model. The results showed that the addition of reinforcements will cause constraint on the plastic flow of ductile matrix, and thus result in no-uniform stress distribution. The reinforcement shape has a pronounced effect on the overall plastic deformation of the metal matrix composites. The loading condition will cause different failure mechanisms of composites. Under tensile loading, the stress-bearing ability in the plastic region is increased with the fiber aspect ratio due to the increase in the interface between the reinforcement and matrix and the decrease in the inter-particle space.

Investigation on mechanical properties of nano-Al2O3-reinforced aluminum matrix composites

In this study, 0.75, 1.5, 2.5, 3.5, and 5 vol.% of alumina nanoparticles were incorporated into the A356 aluminum alloy by a mechanical stirrer and then, cylindrical specimens were cast at 800°C and 900°C. A uniform distribution of reinforcement, grain refinement of aluminum matrix, and presence of the minimal porosity was observed by microstructural characterization of the composite samples. Characterization of mechanical properties revealed that the presence of nanoparticles significantly increased compressive and tensile flow stress at both casting temperatures. The highest compressive flow stress was obtained by 2.5 vol.% of Al2O3 nanoparticles. It is then observed that the flow stress decreases when Al2O3 concentration increased further to 5 vol.% irrespective of the amount of deformation and casting temperature. It was revealed that the presence of nano-Al2O3 reinforcement led to significant improvement in 0.2% yield strength and ultimate tensile stress while the ductility of the aluminum matrix is retained. Fractography examination showed relatively ductile fracture in tensile-fractured samples.

QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS

Dual-Phase (DP) steels are composed of martensite islands dispersed in a ductile ferrite matrix, which provides a good balance between strength and ductility. Current processing conditions (continuous casting followed by hot and cold rolling) generate 'banded structures' i.e., irregular, parallel and alternating bands of ferrite and martensite, which are detrimental to mechanical properties and especially for in-use properties. We present an original and simple method to quantify the intensity and wavelength of these bands. This method, based on the analysis of covariance function of binary images, is firstly tested on model images. It is compared with ASTM E-1268 standard and appears to be more robust. Then it is applied on real DP steel microstructures and proves to be sufficiently sensitive to discriminate samples resulting from different thermo-mechanical routes.

Investigation on microstructural and mechanical properties of microwave processed dissimilar joints

In the present work, microwave joining of stainless steel (SS-316) to mild steel (MS) in bulk form has been successfully carried out using a multimode applicator at 2.45 GHz and 900 W. Principles of hybrid heating were employed using a susceptor medium so as to initiate coupling of microwave with the metals. A nickel based metallic powder was used as a sandwich layer between the bulk pieces. Samples were exposed to microwave radiation in atmospheric conditions. Resulting joints were characterized using field emission scanning electron microscope (FESEM), X-ray diffractometer, microhardness tester and universal testing machine. Microstructure study showed the faying surfaces were well fused and got bonded on either side of the base material. Formation of cementite and metallic carbides were evidenced. The average observed Vickers’ microhardness of core of the joint area was observed to be 133 H v with 0.58% porosity. The ultimate tensile strength of the joint was found to be 346.6 MPa with percentage elongation of 13.58%. Fractography reveals that the joints failed due to both shearing of the brittle carbides and oxides as well as due to plastic flow of the ductile matrix under tensile loading.

Characterization of Nickel Based Alloys (Hard Facing Alloys) with Additions of Ti and Mo

The mechanical engineering industry is always in the search of new hardfacing alloys which nowadays make it possible to solve considerable delicate problems of abrasive wear and corrosion. These alloys are heterogeneous materials and are generally composed of a ductile matrix and a significant proportion in hard phases (carbides, borides or silicides), which give a good wear resistance and corrosion. The following studies made on alloys containing Ni, rich in Silicon and tungsten. We noted that addition of these elements (Si and W) got interesting mechanical properties. The alloys that we chose for this study contain the elements C, B, Si, Cr and W with additions in Ti and Mo. The aim of this work is the characterisation of the various phases formed during solidification, to study chemical affinities in this system poly-constitutes and to make a correlation between the chemical composition, the conditions of development and the microstructures obtained.