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Zhang W.,Institute of Materials Engineering | Zhang W.,Zhejiang University of Technology | Zhang W.,Canny Elevator Co.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2016

Molybdenum (Mo) and high-Cr cast iron mixed powder was laser cladded on the surface of 20 steel substrate under two different scanning speed (100 mm/min and 300 mm/min), and microstructure and hardness of the laser cladding layer with different Mo contents (0.5%, 3%, 5%, 7.5% and 10%) were tested by scanning electron microscope and hardness tester, respectively. The results show that the Mo and high-Cr cast iron laser cladding layer has better properties such as finer grains, higher density without crack and gas hole. When the scanning speed is slower (100 mm/min), the adding of Mo make the crystal grain smaller, the long striped pearlite changed into cellular dendritic austenite. Under different Mo contents, the average hardness of cladding layer is 160, 172, 193, 212 and 226 HV0.2, respectively. When the scanning speed is faster (300 mm/min), the adding of Mo can restrain the growth of carbides and promote long striped original alloy carbides change into square block carbides and lamellar carbides, which is conductive to restrain cracking. Under different Mo contents, the average hardness of cladding layer is 586, 612, 637, 682 and 712 HV0.2, respectively. © 2016, Chinese Mechanical Engineering Society of Heat Treatment. All right reserved.

Zhou Q.,University of Sydney | Blanchard P.,University of Sydney | Kennedy B.J.,University of Sydney | Reynolds E.,University of Sydney | And 9 more authors.
Chemistry of Materials | Year: 2012

Two Ce 3+ containing double perovskites Ba 2CeMO 6 (M = Nb and Ta) have been prepared through the use of mildly reducing conditions, and the Ce valence state has been shown to be +3 through Ce L-edge X-ray absorption measurements. Both oxides adopt a monoclinic structure in I2/m at room temperature and undergo two phase transitions upon heating, a discontinuous I2/m → R3̄ and a continuous R3̄ → Fm3̄m transition. Analysis of the first order I2/m → R3̄ transitions is impeded by the complex peak shapes and diffuse scattering evident in the synchrotron powder diffraction data because of domain wall effects. © 2012 American Chemical Society.

Tillmann W.,Institute of Materials Engineering | Hussong B.,Institute of Materials Engineering | Priggemeier T.,Institute of Materials Engineering | Kuhnt S.,Institute for Mathematical Statistics and Applications in Industry | And 2 more authors.
Journal of Thermal Spray Technology | Year: 2013

The formation of single splats is the foundation for any thermal spray coating. Therefore, this study focuses on the investigation of single splat morphologies to determine the influence of spray parameters on the morphological distribution of particles inside the flame. A new method to create a footprint of a spray jet with an extremely short exposure time was used. The resulting field of splats enabled the assignment of each splat to its radial position in the spray jet. The footprints were analyzed and the quantities and morphologies of the splats were correlated to particle in-flight measurements and coating properties. A strong correlation between the particle velocity, the percentage of the so-called pancake-like splats, and the porosity of the coating could be revealed. The influence of the particle temperature was found to be of minor importance to the splat form and the porosity of the coatings. Still, the particle temperature had a good correlation with the coating hardness and the dissolving of the WC. Measurements of the splat size in different areas of the footprints revealed that the percentage of splats larger than 40 μm in diameter was generally higher in the center of the footprint than in the outer regions. © 2013 ASM International.

Wolf S.,Institute of Materials Engineering | Martin S.,Institute of Materials Science | Kruger L.,Institute of Materials Engineering | Martin U.,Institute of Materials Science
Materials Science and Engineering A | Year: 2014

The influence of strain rate and temperature on the resulting mechanical behaviour of a cast metastable austenitic CrMnNi-TRIP/TWIP steel was investigated. At ambient temperature and below, the formation of α'-martensite dominates causing a pronounced strain hardening. Various analytical models are available in literature and are mostly based on rule of mixture concepts (e.g. Ludwigson and Berger [22] and Narutani et al. [25]). These models were developed for commercial metastable alloys with medium stacking fault energy (SFE). However, for the herein-investigated alloy with very low SFE these models were found to be limited in describing the strain rate dependent material behaviour. A new model is presented predicting the flow stress of metastable alloys incorporating strain rate sensitivity, transformation strain, martensite kinetics and adiabatic heating. © 2013 Elsevier B.V.

Martin S.,Institute of Materials Science | Richter S.,Institute of Materials Science | Decker S.,Institute of Materials Engineering | Martin U.,Institute of Materials Science | And 2 more authors.
Steel Research International | Year: 2011

Dense TRIP-matrix composites containing 5 vol.% Mg-PSZ as reinforcing phase were produced by employing the spark plasma sintering technique. A continuous and seamless interface between the ceramic particles and the steel matrix was achieved. Compression tests revealed better mechanical properties of the 5 vol.% Mg-PSZ-TRIP steel composites in comparison with both, pure and Al 2O 3 reinforced TRIP steel. The underlying deformation mechanism within the austenitic matrix entailed a pronounced martensite formation. An additional phase transformation was observed within the ZrO 2 particles. The enhanced mechanical properties of the 5 vol.% Mg-PSZ composite are dedicated to the transformation strengthening of the ceramic particles. Finally a model of the reinforcing mechanism is proposed. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Decker S.,Institute of Materials Engineering | Lange K.,Institute of Materials Engineering | Dubberstein T.,Institute of Iron and Steel Technology | Kruger L.,Institute of Materials Engineering
Advanced Engineering Materials | Year: 2015

The influence of the sulfur content (0.02 wt%, 0.1 wt%) within the steel phase (16 wt% Cr, 6 wt% Mn, 9 wt% Ni) of a TRIP/TWIP-matrix composite, reinforced with 10 vol% MgO-partially stabilized zirconia (Mg-PSZ), produced by spark plasma sintering (SPS) is investigated. By increasing the sulfur content of the steel phase, the powder particle size after gas atomization is reduced. Hence, the steel/Mg-PSZ-particle size ratio decreases and the distribution of the Mg-PSZ is improved. Within this study, the effect of the sulfur content on microstructure and flow behavior under compressive loading are determined. With increasing sulfur content, the 1% compressive yield strength increases by 40 MPa. The sulfur forms precipitations with chromium and manganese especially at the steel/Mg-PSZ interfaces, which cause a destabilization of the Mg-PSZ during sintering. The destabilization prevents a possible stress-induced phase transformation of the Mg-PSZ. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hussong B.,Institute of Materials Engineering | Pfeiffer J.,Institute of Materials Engineering | Lehmert B.,Institute of Materials Engineering | Wojarski L.,Institute of Materials Engineering | Tillmann W.,Institute of Materials Engineering
Proceedings of the International Thermal Spray Conference | Year: 2013

The presented work compares a new WC-FeCrAl-matrix feedstock powder with a standard WC-Co powder. The investigation covers the powder analysis, spray jet properties, splat flattening and coating properties, as well as, XRD analyses of the feedstock powders and as sprayed coatings. As the formation of single splats sets up the foundation for any thermal spray coating, this step was chosen as the major subject of investigation in this paper. A new method to create a footprint of splats from a spray jet with an extremely short exposure time was used to perform these splat examinations (Ref. 1). It was found, that the interdependencies between spray parameters and coating properties are generally the same for both materials. Differences occurred in the phase stability of the materials during the spraying process. In XRD measurements the standard WC-Co material did not exhibit any recognizable phase transformations of the WC, while a significant formation of W2C and oxidation of the matrix was observed for the WC-FeCrAl powder.

Zenker R.,Institute of Materials Engineering
65th ABM International Congress, 18th IFHTSE Congress and 1st TMS/ABM International Materials Congress 2010 | Year: 2010

The paper describes specific requirements to be met by the beam guiding systems for geometry and material related surface treatment of Al and Mg alloys. For different EB technologies (remelting, densifying, alloying, dispersing) the influence of beam parameters and energy transfer conditions (single- and multi-process technologies) on microstructure of the materials and its properties will be discussed. Under optimum conditions fine grained and homogenous layers with a thickness up to 1.5...5 mm without pores or cracks and with a very good metallurgical contact to the basic material without gaps can be produced. Using multi-process technology in case of EB alloying the maximum hardness of layers on Al alloys AlZnMgCu1.5, AlSi10Mg, as well as AlSi21Ni7Cu3 and AlSi30 achieved values up to 500HV0.1 and wear rate decreases by a factor of 10. The scratch energy density by EB alloying achieves a maximum improvement of factor 10...25. The EB alloying of Mg alloys MgAl9Zn1 and MgAl3Zn1, performed by single- and double-staged processes results in layers thickness up to 3 mm and noteworthy changes of mechanical properties (hardness by factor 4 up to 300HV0.3). In this case corrosion resistance is nearly comparable to those of a rapid solidified Al alloy. Copyright © (2010) by Associação Brasileira de Metalurgia Materiais e Mineração (ABM).

Hussong B.,Institute of Materials Engineering | Lunnemann V.,Institute of Materials Engineering | Tillmann W.,Institute of Materials Engineering
Proceedings of the International Thermal Spray Conference | Year: 2015

In this investigation, the behavior of overlapping HVOF- sprayed WC-Co splats is analyzed. Samples are sprayed and documented in several steps with a low density of splats. This method enables to distinguish between several splats in areas where overlapping clusters of splats occur. The splats are sorted according to their chronological order of impact. With this information, cross sections are made of these clusters to study the porous structure, developing in the center and at the boundaries of the splats. An ion-polishing method was employed to avoid the corruption of small pores and structures by mechanical force. It turns out that pores in HVOF coatings are initiated by the overlapping regions at the edges of the splats. Splats impacting directly onto each other show very dense microstructures at the interface in the center region of the impact. © Copyright (2015) by ASM International All rights reserved.

Decker S.,Institute of Materials Engineering | Kruger L.,Institute of Materials Engineering
Journal of Composite Materials | Year: 2015

A composite reinforced with 5 vol% MgO partially stabilized zirconia and a high-alloyed TRIP-steel matrix (16% Cr, 6% Ni, 6% Mn) was processed. The objective was to trigger a phase transformation under mechanical stresses within the steel and the ceramic. Therefore, the composite was processed by both mixing (110 r/min) and dispersing by intense milling (250 r/min) of the initial powders, and subsequent Spark Plasma Sintering. During Spark Plasma Sintering, the dwell time was varied (5 min, 10 min). The steel/MgO partially stabilized zirconia interfaces were improved through the intense milling and the 10 min dwell time. Furthermore, 50% of the MgO partially stabilized zirconia transformed to the monoclinic phase under quasi-static compressive loading (10-3 s-1) and the composite had a 1% offset compressive yield strength of 665 MPa. Independent from the processing route, 65% of the steel transformed to α′-martensite. © The Author(s) 2015.

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