Renno Veinthal

Mechanical Properties of Kaolin during Heating

Flexural strength (MOR) and Young’s modulus (YM) of Sedlec kaolin were measured using the three point-bending method and modulated force thermomechanical analysis (mf-TMA). Thermal analyses DTA, thermogravimetry and thermodilatometry (TDA). An escape of the physically bound water (20 – 250 °C) strengthens the sample and YM and MOR increase their values significantly. MOR and YM lower their values as dehydroxylation starts at 400 °C. Both quantities, MOR and YM, pass through minimum in the dehydroxylation region (400 – 650 °C). Their next increase is probably caused by the van der Waals forces acting between metakaolinite crystals and by the starting of the solid-state sintering. YM steeply increases above 950 °C as a consequence of the solid-state sintering. A Weibull’s modulus passes through the sharp maximum at the interval 300 – 400 °C.

Characterisation and modelling of erosion wear of powder composite materials and coatings

In erosion wear of composite materials at solid particle impact against the surface, plastic deformation, brittle fracture or combined mechanisms are dominating, depending on the properties of target material surface. Soft metal-matrix of composite materials requires a model of plastic deformation and the ceramic hard phase needs both of the models: the plastic deformation and the brittle fracture model of wear. In this paper, an attempt is made to model the erosion wear of composite materials, to characterise them using indentation method and to correlate calculated erosion rates with experimental results and material parameters.

Determination of Residual Stresses in Thermal and Cold Sprayed Coatings by the Hole-Drilling Method

Residual stresses in most coatings have a significant influence on adhesion, on mechanical properties and on tribological performance. Residual stress can not be measured directly, rather strain is measured and stress is calculated. In this study residual stresses were investigated in thick thermal Ni95Al5 and cold sprayed Ni, Cu, NiZn, AlZn powder coatings using the semi-destructive hole-drilling and layer growing curvature methods. Residual stresses obtained for the thermal spray coating were compressive and with a relatively large deviation of the results indicating the nonuniformity of residual stress. Cold sprayed coatings have more uniform structure than thermal sprayed coatings. Residual stresses were compressive, and results obtained by hole-drilling and curvature method were comparable.

Heat Treatment of Ultrafine Grained AA 6061 Consolidation by Equal Channel Angular Pressing

During the last decade Equal Channel Angular Pressing (ECAP) has emerged as a widely known procedure for the fabrication of ultrafine grained metals and alloys. This review examines recent developments related to the use of ECAP for grain refinement. In the current study the part of capsules wrapper for powder material to be compressed where the powder AA6061 was wrapped in copper sheet and heated at a temperature of 400 OC in hot pressed under the pressure of 400 MPa. Afterward the powder in solid condition was cooled in the air and then does analysis characterization. The sample results of AA6061 are ECAP as is and heat treatment with type Anneal and Artificial Aging (T6) where heat treatment is heated at a temperature of 530 °C for 1 h followed by heating at a temperature of 100 °C for one day and the other for heating at a temperature of 415°C for 2.5 hours followed by heating at a temperature of 177 °C for 8 hours. This paper explains the characteristics of each sample where analyses are based on the mechanism of properties to determine how much change of mechanical properties and microstructure. Heat treatment effect on grain coarsening so that the mechanical properties can be engineered.

Heat Treatment of Ultrafine Grained High-Strength Aluminum Alloy

Aluminum is one of the nonferrous metals with very wide applications. It has unique properties such as light weight and it is ductile has additionally, lower melting point compared to iron. Equal Channel Angular Consolidation (ECAC) is manufacturing method to produce alloys with high strength by consolidation at elevated temperatures. ECAC method can produce a fine grain and combined with oxide inclusion from particle surfaces, high strength. This research will examine the applicability of Equal Channel Angular Consolidation to incorporate aluminum Al 7075 series powder at a temperature of 400OC under pressure of 400 MPa. The effects of heat treatment regimes on grain size of the ECAC samples are observed. The results show hardness of 7075 Aluminum series after ECAC process reaching 120 HV10 and decreases down to 110 HV10 after T6 heat treatment. Hardness further decreases after annealing process, down to 104 HV10. Decline in hardness is accompanied with the increased grain size, which accompanies increased ductility.

Regression Models and Fuzzy Logic Prediction of TBM Penetration Rate

Abstract This paper presents statistical analyses of rock engineering properties and the measured penetration rate of tunnel boring machine (TBM) based on the data of an actual project. The aim of this study is to analyze the influence of rock engineering properties including uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), rock brittleness index (BI), the distance between planes of weakness (DPW), and the alpha angle (Alpha) between the tunnel axis and the planes of weakness on the TBM rate of penetration (ROP). Four (4) statistical regression models (two linear and two nonlinear) are built to predict the ROP of TBM. Finally a fuzzy logic model is developed as an alternative method and compared to the four statistical regression models. Results show that the fuzzy logic model provides better estimations and can be applied to predict the TBM performance. The R-squared value (R2) of the fuzzy logic model scores the highest value of 0.714 over the second runner-up of 0.667 from the multiple variables nonlinear regression model.

Pultruding of Metal Powder Filled Glass Fiber Reinforced Polymer Composites

The present article focuses on manufacturing of metal powder filled pultrusion profiles for electro-technical applications. Herein a set of test material has been reviewed, which was prepared with the aim to present an optimized composite structure with high metal powder content for magnetic slot wedge production, outperforming the products currently available by alternative technology – compression moulding.This article gives a short overview of incorporating fine metal powders as fillers into pultrusion process (including the technical challenges) and the experimental work done in the project. The selection and analysis of components have been briefly discussed along with the results of material tests conducted on prepared composite samples. Mechanical, dielectric and magnetic properties of the samples were studied at different filler loadings and compared to the properties of iron powder filled compressed laminates.Several application specific material properties were determined, including flexural strength according to ISO 178, volume and surface resistivity similarly to IEC 93, and relative permeability using vibrating sample magnetometer (VSM). Scanning Electron Microscope (SEM) and various image processing software were used to analyse the composition and microstructure of the material samples. Material test results are presented at different iron powder loadings from 20 to 55 wt% and recommendations given for optimal materials selection.

Recycled hardmetal-based powder composite coatings: optimisation of composition, structure and properties

Hardfacing is among the most economical methods for surface treatment and service life and efficiency improvement of metal parts subjective to wear. At the same time use of low-cost recycling technologies in the production of powders is of current interest. Focus in this paper is on: a) the production of hardmetal/cermet powders as reinforcements for composite coatings; b) deposition technologies and optimisation of coating structure; c) the wear resistance of coatings at different abrasive wear conditions. The article describes the production and grindability of hardmetal (WC-Co) and cermet (Cr3C2-Ni, TiC-NiMo) powders and their size and shape. Results address the optimisation of the composition and structure of HVOF-sprayed and PTA-welded composite powder coatings based on the commercial spray powders and produced hardmetal/cermet powders. The abrasive wear resistance of coatings at different wear conditions (rubber wheel, erosion and impact wear tests) is analysed.

Structure and Magnetic Properties of NdFeB Powder Prepared by Hydrogen Decrepitation and High-Energy Ball Milling

An ingot of NdFeB alloy was disintegrated by hydrogen decrepitation (HD). High-energy ball milling technique with hard metal milling elements and balls was employed to refine HD powders down to particle size optimum for magnet processing. The experiments were performed according to experimental plan to optimize the milling parameters regarding particle size, contamination and magnetic properties of the powder. The effect of milling time, speed of rotation, ball-powder weight ratio (BPR) and amount of wet agent was investigated. The highest influence was shown to be from attritor speed of rotation, ball-to powder ratio and combined effect of milling wet agent and rotating speed. Unified parameter of estimated number of total ball impacts was calculated, which allows predicting the final particle size of the powder at different milling speeds. Magnetic moments of powders were measured.

Measurement of Residual Stresses in the Cold-Rolled Fe-Ni-Mn/Invar Thermo-Bimetallic Plate

The paper presents a method for measuring residual stresses in normal thermo-bimetal Fe-Ni-Mn/Invar strips with a thickness of 0.76 mm. For this purpose, a setup was designed which permits to remove layers from a strip substrate by electrochemical etching. Residual stresses in the directions that are longitudinal and transversal to rolling are determined by the curvature method based on the layer growing/removing techniques. As a reference, residual stresses were also determined by hole-drilling technique. Tensile and compressive residual stresses arose both in active and in passive layers and were considerably higher when determined by the hole-drilling technique.