Papers by Keyword: Metal Matrix Composite (MMC)

Abstract: In recent years, increasing weld strength along with improved surface properties of the joint during friction stir welding (FSW) has gained noteworthy attention due to increasing applications concerning higher wear resistance and strength related factors. Accordingly, the exploration endures for new materials and ways which will probably increase weld strength along with imparting various improved surface properties to the weld. In spite of several modifications on FSW, its in-situ composite fabrication potential remains quite unfamiliar. In this study, we make available an up to date review of recent in-situ fabricated composites during FSW by using various reinforcements. In particular, the effect of various reinforcements and methodology on the weld strength and surface hardness is reported systematically. Moreover, the strengthening mechanisms accountable for the improvement in weld propeties have been reviewed, and the new potential applications of this new welding strategy are envisaged.

Abstract: Ni-based superalloys, in both single and polycrystalline varieties, are extensively used in high pressure turbine blades. But contrary to single crystal variants, the polycrystalline forms present easier manufacturing and offer higher potential for improvement in metal matrix composites (MMCs). To benefit from this opportunity, an Inconel X-750 superalloy reinforced with TiC particles is proposed, having a polycrystalline microstructure and the possibility for weight reduction in turbine elements application. The metallic powder with an addition of 15 vol.% of 3.7 μm_d TiC particles was prepared through low energy mixing, uniaxial pressing and sintering, followed by a triple heat treatment. The microstructure was analyzed with SEM and XRD techniques. Compressive creep tests were performed at 800 °C with 200 MPa, on both original and reinforced alloys. The study shows how the inclusion of a highly compatible particle reinforcement does not only improves the creep resistance, but also reduces the material weight, thus having potential to promote further reduction in the creep rate on turbine blades submitted to centripetal forces.

Abstract: Magnesium powder in micron scale and various volume fractions of SiC particles with an average diameter of 50 nm were co-milled by a high energy planetary ball mill for up to 25 h to produce Mg-SiC nanocomposite powders. The milled Mg-SiC nanocomposite powders were characterized by scanning electron microscopy (SEM) and laser particle size analysis (PSA) to study morphological evolutions. Furthermore, XRD, TEM, EDAX and SEM analyses were performed to investigate the microstructure of the magnesium matrix and distribution of SiC-reinforcement. It was shown that with addition of and increase in SiC nanoparticle content, finer particles with narrower size distribution are obtained after mechanical milling. The morphology of these particles also became more equiaxed at shorter milling times. The microstructural observation revealed that the milling process ensured uniform distribution of SiC nanoparticles in the magnesium matrix even with a high volume fraction, up to 10 vol%.

Abstract: Short fibre reinforced aluminium was produced using the Temconex^® process which is a continuous extrusion using a mixture of metal powder and ceramic short fibre as feedstock. The Temconex^® process was derived and further developed from the Conform^TM process which uses metal rod rather than powder as feedstock. In the present paper the effect of the prechamber length on the mechanical properties was examined. As material Al99.7 powder with different volume fractions of milled carbon fibres was used. Distribution, orientation and geometry of the embedded fibres were examined using light microscopy. The mechanical properties were determined via tensile testing and resonance frequency analysis. An important increase of the Young’s modulus is observed because of the introduction of fibres. It can be rationalized based on Clyne’s Shear Lag model. Results show that an extension of the prechamber enhances the Young’s modulus and the elongation of fracture due to reduced fibre fracture and better fibre alignment.

Abstract: Aluminium-Matrix-Nanoparticle-Composites were produced by ball milling of micro scale Aluminium powder with various nanoscales ceramic powders like Silicon Carbide, Alumina and Boron Nitride with subsequent consolidation by hot extruding. The composites were investigated by amplitude dependent damping tests, tensile tests at elevated temperatures, hardness measurements, imaging methods and electric conductivity tests. All tested samples were machined out of hot extruded rods. The Amplitude dependent damping of bending samples was determined by measuring the strain dependent logarithmic decrement of free decaying vibrations of bending beams at room temperature. These tests were done after successive step by step isochronal heat treatments. Some samples show substantial improvement of the mechanical properties due to dispersion hardening or grain refinement. It can be concluded that the results are mainly influenced by dislocation effects like Orowan-effect, work-hardening, grain-size-hardening, recrystallization, and creation of dislocations at ceramic particles due to thermal mismatch. Moreover some results can be attributed to fatigue during mechanical cycling namely crack nucleation, crack growth and fraction. The electric conductivity was measured indirectly by permeability tests with a digital hysteresis recording devise. The results show the low influence of nano-particle dispersion hardening to conductivity in comparison of work-hardening.

Abstract: Recently, the attention paid to Metal Matrix Composites (MMCs) has increased markedly. In particular, particle-reinforced MMCs are outstanding due to superior specific properties and their wear resistance. In order to further improve material utilization, recent investigations with local reinforcements in highly stressed component sections, the so-called Functionally Graded Metal Matrix Composites (FGMMC), are concerned. The production of such FGMMC was realized with composite peening - a modified process on the basis of micro shot peening. Due to this solid-phase process, ceramic particles can be introduced into regions close to the boundary layer. As preliminary studies on tin show, ceramic particles can be introduced close to the specimen surface even at room temperature. By varying process parameters, in particular by increasing the temperature, the penetration depth of the particles can be significantly increased. In case of aluminium as base material, an input of particles into the surface could be observed at a process temperature of 150 °C. The combination of aluminium with reinforced ceramic particles makes this process interesting for lightweight, wear-resistant and cyclically highly stressed structural components. Using composite peening to produce FGMMCs is a novel, economic approach.

Abstract: In this work, the “4M-System” (Machine for Multi-Material-Manufacturing) has been developed by RHP Technology for the manufacturing of Titanium Metal Matrix Composites. This equipment allows the Additive Layer Manufacturing (ALM) of large structures and uses a Plasma Transferred Arc (PTA) as a heat source for depositing feedstocks (powder/wire) layer by layer onto a substrate. Test coupons, made of Titanium powders and having different concentrations of B₄C particles, were deposited to form Metal Matrix Composites. Various processing parameters such as deposition rate, travel speed of the torch as well as plasma parameters (power/current/gas flow) were assessed for getting pore- and crack-free samples. After deposition, the specimens were cut and the cross-sections were analysed by optical- and scanning electron microscopy. Furthermore, the hardness, Young’s Modulus, and tensile strength were measured. Ti-Metal Matrix Composite materials resulted in higher strength and Young´s Modulus in comparison to the pure Ti-metal matrix. Using the 4M-System, B₄C particle reinforced Ti-MMC’s were successfully manufactured. Thus the 4M-System proved the capability of joining multi-material concepts, which also promises to create graded concentrations of reinforcement in the material.

Abstract: Metal matrix composites with ceramic reinforcements such as particles or fibers have come into focus during the past decades due to rising requirements on engineering materials. In this work, composite materials out of high-alloy CrMnNi-steel matrices with varying Ni-contents (3 wt.% and 9 wt.%) and 10 vol.% Mg-PSZ were processed by hot-pressing. The variation in Ni-content resulted in a change in stacking fault energy (SFE) which significantly influenced the deformation mechanisms. The mechanical behavior of the developed composites was investigated in a wide strain rate range between 0.0004 s^-1 and 2300 s^-1 under compressive loading. This was done by a servohydraulic testing system, a drop weight tower, and a Split-Hopkinson Pressure Bar for the high strain rates. To study the influence on the deformation mechanisms such as martensitic transformations and/or twinning, interrupted tests were also carried out at 25 % compressive strain. Subsequent microstructural examinations were done by a magnetic balance to measure the quantity of α’-martensite as well as by scanning electron microscopy (SEM). The results show an increase of strength and strain hardening with decreasing SFE of the matrix due to increased α’-martensite formation. The addition of the Mg-PSZ particles resulted in further strengthening over almost the entire deformation range for all investigated composites. At high strain rates quasi-adiabatic heating suppressed the martensite transformation and reduced the strain hardening capacity of the matrix. Nonetheless the particle reinforcement retains its strengthening effect.

Abstract: Metal matrix composites (MMC) are often applied to tool surfaces to increase resistance to wear and tear. However, some matrix and particle materials such as Ni, Co, WC or TiC are expensive and partly classified as critical elements. With respect to tribo-mechanical properties, Fe-alloys reinforced with oxide particles are promising compound materials to produce wear-resistant MMC with low-cost and readily available materials. However, thus far the technical application of such MMCs is limited due to poor wettability of the oxides by Fe-base melts and an associated weak bonding between the oxide particles and the metal matrix phases. In this work two novel production techniques (namely pre-metallization and active sintering) are introduced, which improve the wettability and interfacial reactions between both materials and therefore enable supersolidus liquid-phase sintering (SLPS) of the MMC. For the first technique the oxide particles are pre-metallized by depositing a thin film of TiN on the surfaces. The second technique is called active sintering. For this technique the alloy design is adapted from active brazing, so that wettability of the oxide particles by the alloy-melt is increased. The resulting effects of these techniques are investigated using wetting and sintering experiments, and are analyzed with respect to the developed microstructures and interfacial reactions between the oxide particles and the metallic phases.

Abstract: High mechanical loads, corrosion, and abrasion decrease the lifetime of tools. One way to increase the wear resistance of tool materials can be achieved by adding hard particles to the metal matrix such as titanium carbide, which protect the softer metal matrix against abrasive particles. This material concept is designated as metal matrix composite (MMC). Ferro-Titanit^® is such MMC material, possessing high wear and a simultaneously high corrosion resistance, for which reason this material is used in the polymers industry. The material concept is based on a corrosion-resistant Fe-base matrix with up to 45 vol% titanium carbide (TiC) as a hard particle addition to improve the wear resistance against abrasion. These TiC hard particles must be adapted to the present tribological system in terms of hardness, size and morphology. This study shows how the size and morphology of TiC hard particles can be influenced by the refractory element niobium (Nb). Therefore, the element Nb was added with 2 and 4 mass% to the soft-martensitic Ferro-Titanit^® Grade Nikro128. The investigated materials were compacted by sintering, and the densified microstructure was further characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), and optical image analyses. Furthermore, microstructure and properties of the compacted Nb-alloyed samples were compared to the reference material Nikro128. The results show that the addition of Nb influences the morphology, size and chemical composition of the TiC hard particle. These changes in the hard phase characteristics also influence the materials properties. It was shown that the phase niobium carbide (NbC) is formed around the TiC during the densification process, leading to a change in morphology and size of the TiC.