Strangpressen von verschleißbeständigen Fe‐Basis MMC

Hot extrusion of wear resistant Fe‐base metal matrix composites (MMC) Increasing demands on technical surfaces, i.e. thermal load, corrosion or wear, often prompt the development of tailored materials or coatings. In highly abrasive environments the progress in powder metallurgy has lead to the production of highly wear‐resistant materials based on metal‐matrix composites (MMC). Such materials are produced from a metal matrix (MM) based on Fe, Ni or Co and additional hard phases (HP), such as carbides, nitrides, borides or oxides. Moreover, powder metallurgical techniques can be used to adapt the particle size, the distribution and the content of the hard phases to the wear system on a large scale. HIP cladding is an established method of producing such MMC, but due to its near net shape capsule technique it is quite expensive. Because of this reason hot direct extrusion of capsules filled with powder blends was researched in a DFG‐Project as a method of producing long cylindrical products. Aiming at a high abrasive wear resistance, powder blends of hardenable steels with additions of fused tungsten carbide (WSC) or titanium carbides (TiC) were used. The extruded MMC were investigated with respect to their densification and microstructure, their bending strength and their wear resistance.     

Development of Wear and Corrosion Resistant Metal Matrix Composites with hard Particles formed in Situ

Metal matrix composites (MMC) were developed, consisting of hardenable steel matrices and embedded particles of titanium nitride (TiN) or vanadium nitride (VN) formed in situ during the consolidation by hot isostatic pressing (HIP). Designing wear and corrosion resistant materials was the objective of this development. The materials were produced by means of powder metallurgy and are composed of a ferrritic stainless steel powder X4CrMo15–1 and crushed particles of ferro titanium or ferro vanadium, respectively. These powder mixtures were first heat treated in an N₂‐atmosphere for alloying with nitrogen and subsequently consolidated to wear resistant MMC by HIP. This publication describes the necessary processing steps, taking into account thermodynamic equilibrium calculations with Thermo‐Calc.     

Correlation of processing route and heat treatment with the abrasive wear resistance of a plastic mold steel

The processing of polymers necessitates the use of corrosion and wear resistant tool materials being in direct contact with the feedstock material. Corrosion resistant cold work tool steels, the so called plastic mold steels, are successfully applied here, offering both a good wear and corrosion resistance. The lifetime of this tool depends on the applied heat treatment but also the processing route has a distinct effect on the resulting properties. In this work, different powder metallurgical routes like hot isostatic pressing, build‐up welding (plasma transfer arc (PTA)) and thermal spraying (high velocity oxy fuel (HVOF) and atmospheric plasma spraying (APS)) were applied to produce coatings on low‐alloyed construction steel. Coatings are compared in relation to the changes in microstructure and the feasibility of an adequate heat treatment. This paper discusses strategies to maximize wear resistance in dependence of heat treatment and the microstructural changes arising from the processing.     

Mechanical properties of co‐extruded wear resistant powder metallurgical layers on steel substrates

Materials with high resistance against abrasive wear are of interest for many tool applications. For economical reasons, thick coatings of several millimetres are requested. The cladding of these materials to low alloyed substrates is commonly performed using hot isostatic pressing, being a cost intensive process in particular for long products. Thus, a novel manufacturing route via direct hot extrusion of encapsulated bulk steel bars and presintered tool steel powders was recently developed. In this manner, wear resistant claddings of PM tool steels and wear resistant MMC on steel substrates could be processed. Heating to process temperature leads to presintering of the powder and only a weak bonding between the steel substrate and the powdery layer. However, after direct hot extrusion at 1150 °C an interface free of macroscopic defects is formed between both materials. The quality and strength of this bond zone was investigated by micro tensile, 4 point bending and shear tests for different materials combinations. For high strength substrate materials, failure always occurs in the brittle wear resistant layer and not at the interface. These results are in agreement with microstructural investigations, exhibiting a pore‐ and defect‐free interface dominated by interdiffusion processes.     

Verschleißbeständige Fe‐Basislegierungen mit Niobkarbid

Wear Resistant Fe‐Base Alloys with Niobium Carbide Martensitic Fe‐base alloys from the system Fe‐Cr‐C are widely used as chilled cast irons and tool steels. Because of the low hardness of their FeCr‐carbides this paper reports about new alloys with primarily solidified harder niobium carbides. It focuses on a secondary hardenable welding alloy, a coating material for composite castings, a chilled casting and a corrosion resistant cold work tool steel, which are investigated with respect to their process related microstructure and abrasive wear behaviour.     

构型陶瓷/钢铁耐磨复合材料研究进展

近年来,陶瓷颗粒非均匀分布增强钢铁基复合材料(构型复合材料)由于具有优异的耐磨性,成为国内外高性能耐磨材料研究和应用的热点.对构型复合材料耐磨性的研究进行了综述,认为在无冲击磨料磨损工况下,构型复合材料的耐磨性显著高于常规陶瓷颗粒均匀分布增强复合材料,其耐磨性顺序按照基体排列为:高铬铸铁基>合金钢基>高锰钢基复合材料;陶瓷/钢铁界面结合强,则复合材料耐磨性高;按照陶瓷颗粒排序是:WC>(TiC,ZTA)>Al2O3增强复合材料;ZTA中ZrO2含量高,则耐磨性好.在高冲击磨料磨损工况下,构型复合材料耐磨性远不如无冲击工况下的耐磨性,有的甚至比基体差;合金钢基复合材料耐磨性比高锰钢基稍高.综述了不同工况下构型复合材料的磨损机理,并提出了构型陶瓷/钢铁复合材料的研究方向.     

Neuentwicklungen für den Verschleiß‐ und Korrosionsschutz beim Plasma‐Pulver‐Auftragschweißen

New developments for wear an corrosion protection by weld surfacing with plasma transmitted arc process Highly wear‐resistant claddings which contain carbides can be applied by weld surfacing with the PTA process. The use of vanadium carbide prevents undesirable reactions with the matrix material. Thus, highly corrosion‐resistant Fe‐based claddings can be produced for applications in the food and marine industries, and Ni‐based claddings can be applied to components exposed to inorganic acid attack. A combined test is applied for determining the relative effect of corrosion under combined exposure to abrasive wear and corrosion and indicates the primacy of abrasive wear for behaviour in operation.     

Zum Einfluss des Schweißens auf das Kriechverhalten moderner Stähle für die thermische Energieerzeugung

The influence of welding on creep behaviour of modern steels for thermal power generation Un‐ and low alloyed ferritic/bainitic Chromium steels as well as high alloyed ferritic/martensitic 9–12 % Chromium steels are widely used for high temperature components in thermal power generation. Welding in all its variety is the major repair and joining technology for such components. The weld thermal cycle has significant influence on the base material microstructure and its properties. The Heat Affected Zone is often regarded as the weakest link during high temperature service. While weldments of un‐ and low alloyed ferritic Chromium steels can show significant susceptibility to Reheat Cracking in the coarse grained heat affected zone, weldments of high alloyed ferritic Chromium steels generally fail by Type IV Cracking in the fine grained heat affected zone during long term service. In this paper the influence of the weld thermal cycle on the base material microstructure is described. Long‐term creep behaviour of weldments is directly related to the main failure mechanisms in creep exposed ferritic weldments and implications for industries using heat resistant ferritic steels are shown.     

Verschleißbeständige induktiv hergestellte Beschichtungen (InduClad)

The lifetime of abrasive stressed components can be extended by coating. Deposition welding and also the new method InduClad are suitable procedures for the production of thick layers. Both these technologies were compared and their advantages and disadvantages were assessed. The results from wear investigation are considered as a final evaluation. Special attention will be paid to material‐technique aspects of the application of welding technology previously unusable like ionic or covalent bonded hard materials. Also, alternatives are presented to conventional metal‐matrix‐composites and especially the embedding of hard materials in metallic matrices will be evaluated. The results of wear tests in laboratory and real environment will help to evaluate the embedding of such not metallic hard materials. The thermal stress of the hard materials is significantly lower with InduClad than with typical arc processes. It successfully avoided the floating of the relative light hard materials. We will present the first application examples of not metallic materials in abrasive wear protection technology.     

Advanced cold rolled steels for automotive applications

Advanced multiphase steels offer a great potential for bodies‐in‐white through their combination of formability and achievable component strength levels. They are first choice for strength and crash‐relevant parts of challenging geometry. The intensive development of high‐strength multiphase steels by ThyssenKrupp has led to hot dip galvanizing concepts with an outstanding forming potential. Hot rolled, hot dip galvanized complex phase steels are currently produced in addition to cold rolled DP and RA steels. New continuously annealed grades with tensile strength levels of up to 1000 MPa in combination with sufficient ductility for applications mainly in the field of structural automobile elements make use of the classic advantages of microalloying as well as the principles of DP and TRIP steels. Further improvement of properties will be reached by the new class of high manganese alloyed steels.     

Mikrostruktur‐Untersuchungen zum Schwingungsverschleißverhalten von Nickelkomposit‐ und Ni‐P‐Schichten

Microstructural and oscillating sliding wear studies of nickel composites and electroless Ni‐P layers In many industrial applications, oscillating sliding wear leads to serious damage of construction components. To avoid this, different layers of electroplated nickel and nickel composites as well as chemically deposited nickel phosphorus layers are used and/or tested. The performance of these layers under oscillating sliding wear was characterized. Additionally microstructure characterisations took place regarding grain size, particle content and distribution as well as concerning crystallization and development of tetragonal phase nickel phosphide. These results correlate well with the Martens hardness of the layers and contribute to understand the oscillating sliding wear characteristics of the examined layers. Heat treated Ni‐P layers achieve twice the hardness of nickel dispersion layers; however, fail under oscillating sliding stress by embrittlement, cracking and debonding. On the other hand dispersion‐hardening nano composites with TiO₂ clearly exhibit a more favourable tribological behaviour. A solid content of approx. 3 vol‐% leads to dispersion and fine grain hardening effects, which cause good protection against oscillating sliding wear; thereby the Ni‐matrix remains ductile. The incorporation of very hard particles (SiC) intensifies the oscillating sliding wear process due to the abrasive effect of the particles.     

粉末冶金制备工艺对TiC增强高铬铸铁基复合材料性能的影响EI北大核心CSCD

采用高能球磨和真空烧结的方法制备TiC增强高铬铸铁(HCCI)基复合材料。利用SEM,DSC等方法对不同球磨时间的粉末进行分析,研究不同烧结温度对高铬铸铁基复合材料的显微组织、硬度及密度的影响,比较相同工艺下复合材料与高铬铸铁材料的耐磨性。结果表明:球磨12 h后的粉末颗粒大小趋于稳定,粉末活性提高,烧结性能改善,烧结试样中TiC均匀地分布在基体中。随着烧结温度的升高,复合材料内部晶粒逐渐长大,密度和硬度逐渐提高。在1280℃超固相线液相烧结的条件下烧结2 h后,致密度达94.17%,硬度和抗弯强度分别为49.2HRC和980 MPa。在销盘磨损实验中复合材料的耐磨性为单一高铬铸铁材料的1.52倍,磨损机制为磨粒磨损+轻微氧化磨损。     

Drehen und Fräsen pulvermetallurgischer Hartlegierungen für warmgehende Werkzeuge

Turning and Milling of Powder Metallurgical Hard Alloys for Tools in Hot Working Applications Hard metals are high wear resistant materials. The microstructure of these composites consists of hard phases which are embedded in a metal matrix. The high hardness and the high content of the hard phases lead to a difficult machining of these materials. The present study investigates the turning and milling of D3 cold work steel (X210 Cr 12) and the powder metallurgical Fe‐based alloys ASP60 and ASP23 + WC/W₂C. The cutting tool materials were polycrystalline cubic boron nitrides (CBN) and ceramic inserts. The machining process could be judged by means of tool wear and machining quality (surface roughness and changes in the surface near zone). The investigations illustrate that the machinability of the different hard metals depends on the cutting speed and the cutting tool material.     

Elektronenstrahl‐Randschichtbehandlung für die Herstellung verschleißbeständiger Auftragschichten auf nichtrostenden Stählen

Stainless steel components exposed to mechanical stresses are subjected not only to corrosion, but to abrasive wear. There are several possibilities for enhancing the wear resistance of stainless steels; however, such processes are very often associated with a reduction in corrosion resistance. This paper presents an electron beam surface treatment technology to significantly improve the wear resistance of austenitic steels (e.g. X6CrNiMoTi17‐12‐2) and duplex steels (e.g. X2CrNiMoN22‐5‐3), without a negative influence on the corrosion behavior. Fe‐ and Co‐additive wires were deposited thermally by electron beam cladding. The cladding layers produced were free of defects such as cracks and pores, and were well metallurgical bonded to the base materials. Microstructural analysis, hardness measurements, wear tests and corrosion tests were carried out. The wear rate k was reduced by a factor of 100 compared to the base materials for electron beam cladding with Fe‐based wire and by a factor of 10 with Co‐based wire. Corrosion resistance was preserved for the Fe‐based cladding layers and slightly increased (by a factor of 3) for the Co‐based cladding layers.     

Microstructural study and densification analysis of hot work tool steel matrix composites reinforced with TiB2 particles

Hot work tool steels are characterized by good toughness and high hot hardness but are less wear resistant than other tooling materials, such as high speed steel. Metal matrix composites show improved tribological behavior, but not much work has been done in the field of hot work tool steels. In this paper TiB₂-reinforced hot work tool steel matrix composites were produced by spark plasma sintering (SPS). Mechanical alloying (MA) was proposed as a suited process to improve the composite microstructure. Density measurements and microstructure confirmed that MA promotes sintering and produces a fine and homogeneous dispersion of reinforcing particles. X-ray diffraction patterns of the sintered composites highlighted the formation of equilibrium Fe₂B and TiC, as predicted by thermodynamic calculations using Thermo-Calc® software. Scanning electron microscopy as well as scanning Kelvin probe force microscopy highlighted the reaction of the steel matrix with TiB₂ particles, showing the formation of a reaction layer at the TiB₂-steel interface. Phase investigations pointed out that TiB₂ is not chemically stable in steel matrix because of the presence of carbon even during short time SPS.     

Neue Kapseltechnik für Diamantverbundwerkstoffe mittels PVD‐Verfahren

Novel encapsulation technique for diamond composites using PVD‐process For machining of mineral materials diamond tools consisting of a steel body combined with diamond impregnated segments are used. Frequently, these segments are hot pressed. Other process routes are pressureless sintering of green compacts partly combined with hot isostatic pressing and hot isostatic pressing of encapsulated powder mixtures. The compaction effect of hot isostatic pressing require a low porosity of sintered components realized by using ultra‐fine metal powder or an impermeable capsule made of metal or glass. The Institute of Materials Engineering pursues a novel process route by physical vapor deposition of a coating on pressureless sintered composites. The thin coating acts as a capsule and guarantees the pressure transfer in the following hot isostatic pressing process. Although bronze powders with particle sizes up to 90 μm are used, the manufacturing of diamond composites with low porosities is possible. In comparison to conventional encapsulation‐techniques the main advantages of this novel process route are the use of comparatively coarse metal powders and a larger geometric flexibility.     

Characterization of mechanical properties and three‐body abrasive wear of functionally graded aluminum LM25/titanium carbide metal matrix composite

Several engineering components require location specific performance under operating conditions. A compositional/microstructural gradient can provide the performance required at specific locations and these materials were named as functionally graded materials. Functionally graded aluminium metal matrix composites were generally established for the tribo‐components where high wear resistance was a necessity. Reports on three body abrasive wear behaviour of functionally graded materials was limited to date. In the present work, a new functionally graded system comprising aluminium/titanium carbide (10 wt%) was produced through stir casting route followed by centrifugal casting technique and its three body abrasive wear behaviour was investigated. Hollow cylindrical part with the dimensions of length 150 mm, outer diameter 150 mm and thickness 16 mm was obtained. Microstructural study was performed on outer (1 mm) and inner surface (13 mm) to analyze the compositional gradient across the thickness of the functionally graded composite. Hardness was measured on different surfaces along the radial distance from outer periphery and tensile test was conducted on the outer and inner zone. Abrasive wear test was conducted on different surfaces of the functionally graded composite under various loads and speeds at constant time. The microstructural results revealed that particle segregation was more at the outer surface and less at the inner surface. Wear test results showed that increase in wear rate was obtained with increase of load and decrease in wear rate was obtained with increase of speed. The outer surfaces of the functionally graded composite had greater mechanical properties and better wear resistance compared to other surfaces. Scanning electron microscopy analysis was done on the abraded surfaces and observed wear mechanisms were interpreted.     

Herstellung verschleißbeständiger Metallmatrix‐Verbunde auf Fe‐Basis

Production of Wear Resistant Metal Matrix Composites on Fe‐base The hot isostatic pressing process allows the production of Metal Matrix Composites (MMC) with excellent abrasive wear resistance. Because of high manufacturing costs three alternative productions routes are introduced. It is shown that presintered powder capsules filled with steel powder and hard phases (up to 30 vol.‐%) can be extruded to rods reaching the theoretical density. Coated flat products were produced by roll compaction of certain powder capsules. Using sintering experiments with a constitutional liquid phase (supersolidus liquid phase sintering) shows that even gas atomized prealloyed steel powders can be densified without any pressure.     

Thermisch gespritzte titankarbidverstärkte Eisenbasisschichten als Alternative zu konventionellen karbidischen Werkstoffen

Thermal sprayed titanium carbide strengthened iron coatings as alternative for conventional carbide materials High velocity oxygen fuel (HVOF) sprayed carbide based materials are industrially well established as wear and corrosion protection coatings. Because of the high carbide content of typically 75 weight percent and more they are providing a very high hardness and excellent wear resistance. However, at the same time this characteristic is resulting in major difficulties during post‐processing steps. Cost‐effective machining processes such as turning and milling are usually not applicable and any sprayed oversize has to be reduced by grinding. To overcome these drawbacks a novel carbide‐based material concept, which is already in use for sintering processes, is offering promising properties. Titanium carbides at a reduced content of 33 weight percent embedded in a ferrous matrix can provide distinctly improved characteristics for optimal machinability. Depending on the carbon content the iron‐base material can additionally offer a temperable matrix for enhanced wear behaviour. Within this study spray trials have been carried out to investigate the sprayability of titanium carbide strengthened iron powders with a gaseous and a liquid fuel driven high velocity oxygen fuel spraying system. Optimised parameters were developed by implementing the statistical method of design of experiment (DoE). The resulting coatings were analysed with respect to microstructure, hardness and phase composition and compared to sintered reference materials. Furthermore thermally sprayed iron‐based coatings strengthened with titanium carbides were heat treated to proof the retained temperability of the iron matrix after thermal spray processing.