Key Engineering Materials Vol. 742

Abstract: Fiber-reinforced plastics (FRP) are of great importance for the transport sector, the aerospace industry, for wind power plants, in the building sector and in the field of sports and leisure applications. Optimization of the adhesive bonding process for FRP structures, especially the surface preparation prior to bonding, will be of a central importance in forthcoming expansion of FRP use. In this connection the key problem depends on the FRP polymer matrix. In the case of duroplastic matrix the main problem is the presence of release agent on the surface of joining components. For the thermoplastic matrix such as polypropylene (PP), the main problems are the low surface energy and the inertness of its surface. Conventional pretreatment methods, such as manual grinding, shall be replaced by energetic radiation technics like VUV lamps (vacuum ultraviolet spectral range: 100 – 200 nm). This approach is a non-contact method, characterized by high treatment homogeneity and material-saving properties, combined with no further fibers to be released. The surface of the thermoplastics is activated by the incorporation of oxygen, release agent contamination on the thermoset is cleaned or modified [1 - 8]. The results of the VUV surface activation of PP and CFRP with regard to the incorporation of functional groups, increase of surface energy, matrix degradation and the adhesion increase of adhesive bonds are presented. In addition, studies on the release agent coating and the release agent modification by VUV radiation are presented. The work is completed by considerations concerning possibilities to accelerate the process (in particular, wavelength dependence, influence of an inert gas or the moisture content). Finally, an evaluation of the VUV pretreatment is carried out on the basis of two specific applications.

Abstract: This study focused on the examination of unsaturated polyester resin based continuous glass filament mat reinforced composites (GFRP) and the modification by core-shell rubber particles (CSR). The goal was to evaluate the effect of CSR toughening on processability, mechanical properties and impact strength as well as the interaction with inorganic color particles in the submicron range on the GFRP. The interlaminar fracture toughness G_Ic of the modified GFRP was improved by about 20% compared to the neat GFRP by using only 2 wt-% of the CSR modifier, while only marginally increasing the viscosity of the reactive mixture. The responsible mechanisms were found to be local shear yielding of the matrix and an improved fiber-matrix adhesion. The hybridization of inorganic color particles and CSR reduced the interlaminar fracture toughness of the laminate, which could be ascribed to the formation of pores due to the introduction of the oxide particles. However, the impact behavior of the GFRP was positively affected.

Abstract: The injection molding process is an economical process for manufacturing of thermoplastic components. Complex geometries can be realized with high automation and short cycle times. However the mechanical properties of injection-molded parts are not suitable for mechanical demanding components even by adding short or long fibre. As bold connections are used frequently for load transfer, the load introduction area particularly is limited by low bearing strength. The present paper shows the influence of tailored inserts based on continuous fibre on the bolt-loaded hole of injected test specimen.

Abstract: A flexible and individual component manufacturing process for thermoplastic composites (TPC) has been developed at the Institut fuer Kunststoffverarbeitung in Industrie und Handwerk an der RWTH Aachen (Institute of Plastics Processing (IKV) at RWTH Aachen University). The process consists of a quality controlled tape production and a combined forming and joining process with additive manufactured functional structures. This paper describes the requirements for the unidirectional (UD) tape properties and the quality controlled tape production line in order to allow for a flexible and individual component manufacturing of load optimised thermoplastic composite parts. Besides the UD tape geometry and fibre impregnation quality an even fibre distribution over the width of the UD tape is an important characteristic. Results of investigations regarding the online measured quality data (fibre distribution) and offline measured UD tape properties (local fibre weight content) are presented and discussed.

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.

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: 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: In the present work, in situ reinforced titanium composites (TMCs) synthesized using inductive hot pressing (iHP) are studied. The effects of B₄C phases and applied processing conditions, on the microstructure and properties of TMCs, are investigated. With the addition of B₄C particles, the microstructure of TMCs is refined and the strength is improved.Products of reactions which occur during the manufacturing process are analysed in detail. Microstructure observation illustrates, that B₄C survives - depending on the processing conditions. The reinforcing phases are homogeneously distributed in Ti matrix. Moreover, results of densification, mechanical properties and hardness measurements help to identify the most suitable processing conditions to produce this kind of TMCs.

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: 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.