Wojciech Z. Misiolek

Consolidation of metal powders during the extrusion process

Abstract The extrusion of metal powders at room temperature without subsequent sintering allows manufacturing of final products with unique microstructures and therefore with unique mechanical properties. In this study, the experimental results of extrusion of both aluminium and copper powders under laboratory conditions are presented and analysed. The main objective of the work is to demonstrate that both aluminium and copper can be consolidated in extrusion from loose powder to highly dense products. The influence of the powder material characteristics and compaction pressures on final density and microstructure are investigated. Quantitative and qualitative metallography has been applied to give more insight into the final porosity level and its distribution within the remaining part of the unextruded billet and within the extrudate.

Correlations between microstructure and surface properties in a high nitrogen martensitic stainless steel

Nitrided and tempered AISI 410S stainless steel was tested under corrosion–erosion conditions and compared to conventional AISI 420 martensitic stainless steel. The corrosion–erosion resistance of the nitrided specimens was higher than that of the AISI 420 steel when tempered at 200 °C, but it decreased with tempering temperature in the range between 200 and 600 °C. The higher corrosion–erosion resistance of the high-nitrogen steel was credited to a more homogeneous distribution of chromium in martensite and a lower number of coarse second-phase particles, especially for tempering temperatures below 550 °C. The hexagonal -nitride was identified in specimens tempered at 200 °C, while finely distributed cubic CrN nitrides were observed in specimens tempered between 400 and 600 °C. Hexagonal Cr2N nitrides were observed at 550 and 600 °C. These coarse, high-chromium precipitates were responsible for the drop in corrosion resistance of the nitrided specimens.  2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Reactive sintering and reactive hot isostatic compaction of aluminide matrix composites

Abstract Reactive powder-processing techniques involve use of a transient liquid phase for the formation of a compound. Two variants of reactive synthesis have been successfully applied to the fabrication of aluminide matrix composites. In certain systems it is possible to react mixed elemental powders directly to form a nearly full density structure (such as Ni3Al and NbAl3). This approach is applicable to systems with sufficient adiabatic heating from the reaction exotherm to induce densification by liquid phase sintering. In systems with lower reaction enthalpies, an alternative involves the application of an external stress during the reaction. The two main variants illustrated here are hot isostatic compaction of mixed elemental powders (nickel + aluminum) or hot isostatic compaction of partially reacted powders (TiAl). From this base it is possible to identify the best processing approach based on the system thermodynamics.

Fluid Performance Study for Groove Grinding a Nickel-Based Superalloy Using Electroplated Cubic Boron Nitride (CBN) Grinding Wheels

The performance of three water-based grinding fluids was analyzed and compared to a neat oil tested under the same process conditions. Light optical and scanning electron microscopy observations show the mechanism of metal deposition that leads to CBN wheel failure for water-based fluids. To improve the performance of the water-based fluids, a new nozzle layout is proposed that would prevent metal deposition on the CBN wheels. The proposed solution is not chemical, but mechanical in nature and the presented setting should be optimized in the future to assure satisfactory performance of the CBN wheels with water-based fluids.

Evaluation of Nano-porous Alumina Membranes for Hemodialysis Application

Globally, kidney failure has consistently been a major health problem. The number of patients suffering from kidney failure is radically increasing. Some studies forecast an exponential growth in the number of kidney failure patients during the coming years. This emphasizes the importance of hemodialysis (HD) membranes. Current dialysis membranes (cellulose based and synthetic polymer membranes) have irregular pore shapes and sizes, nonuniform pore distribution and limited reusable capability, which leads to low efficiency of toxin removal. New alumina membranes with uniform, controllable and well-structured nanoscale pores, channeled pores aligned perpendicular to the membrane plane, high porosity, high thermal and chemical resistance, and better mechanical properties are certainly preferable to currently used membranes. Determination of transport properties of alumina membranes will assist in the development of the alumina membranes for enhancing hemodialysis. Experiments were performed to evaluate hydraulic permeability, solute diffusive permeability, sieving coefficient, and clearance of four solutes (urea, creatinine, Vancomycin, and inulin) for alumina membrane. Based on comparison of these values against those of polyethersulfone (PES) membranes, transport performance of alumina membrane was determined. Hydraulic conductivity of the alumina membrane was approximately twice that of the PES membrane and inulin sieving coefficient for alumina membrane is approximately 21% higher than that for PES membrane. Alumina membrane has higher solute clearances and no albumin leakage, which makes it an effective replacement for current dialysis membranes.

Effects of homogenisation treatment on microstructure and hot ductility of aluminium alloy 6063

Abstract Several homogenisation treatments were applied to direct chill (DC) cast ingots of aluminium alloy 6063, in order to analyse the resulting microstructures developed from these diverse conditions and their effects on the hot ductility of this alloy. Imaging was performed using scanning electron microscopy (SEM) and a focused ion beam (FIB) instrument. These techniques identified variations in distribution and morphology of second phase particles (AlFeSi and Mg2Si). FIB results for the various AlFeSi particles correctly identify their shapes in three dimensions (3D). The particles were identified by energy dispersive spectroscopy (EDS) in the SEM, and by X-ray diffraction (XRD) for bulk samples. Hot tensile testing (HTT) was conducted between 470 and 600°C to asses the hot ductility for each condition. The inferior ductility of as cast samples was due to the poor bond strength of the β AlFeSi phase at the grain boundaries. Homogenised samples, which contain α AlFeSi, exhibited improved ductility. Samples that were water quenched following homogenisation were absent of Mg2Si precipitates, when these elements remained in solid solution. These exhibited the highest ductility.

Material physical response in the extrusion process

Abstract The mechanical properties and surface quality of the extruded profiles depend on the final microstructure which has been developed during the extrusion process. The final microstructure is a result of a billet microstructure, material deformation history and post-processing treatment. In order to understand the role of the metal flow in the deformation history both physical and numerical process modelling techniques have been applied. Physical modeling of the extrusion process using modelling materials allows quick and inexpensive evaluation of the flow conditions through different die configurations. Additional information can be obtained from the crystallographic characterization of the typical deformation zone regions such as dead metal zone, main deformation zone and recrystallized zone on the billet-container interface. The electron backscattering diffraction (EBSD) technique has been utilized to follow in detail the orientation aspects of the deformed grains in extruded aluminum. This analysis provides information which can be utilized in the die and process design to improve metal flow uniformity and therefore the microstructure of the final product. It also allows prevention of the typical extrusion defects like surface tearing.

Rapid prototyping of extrusion dies using layer-based techniques

Extrusion die design and development often requires significant craftsman skill and iterative improvement to arrive at a production-ready die geometry. Constructing the dies used during this iterative process from layers, rather than from one solid block of material, offers unique opportunities to improve die development efficiency when coupled with concepts drawn from the rapid prototyping field. This article presents a proof-of-concept illustrating the potential utility of layer-based extrusion dies for the die design and fabrication process. The major benefits include greater flexibility in the design process, a more efficient, automated fabrication technique, and a means for performing localized die modifications and repairs.

Three-dimensional material flow analysis of asymmetric hollow extrusions

Abstract All tube manufacturing processes induce some degree of eccentricity, as a result of the particular extrusion technique, combined with imperfect control of the process parameters. An eccentric tube is identified when the difference between the maximum wall thickness minus the minimum thickness is greater than zero. This is a typical problem for higher melting point materials including Zr, Cu, Ti and Fe and their alloys, where porthole die arrangements cannot be used. The major causes of tube eccentricity in extrusion have been analyzed in the past, and conclusions based on the results for stainless steel tubing are available in the literature. An additional degree of complexity is introduced when the extrusion profile is hollow and asymmetric. To study the complex flow through these dies, the physical modeling technique has been implemented, with the objective to optimize homogeneous flow within the billet in front of the extrusion die, and to correct for extrudate curvature. This is accomplished by examining the impact of general parameters of direct extrusion through non-axisymmetric hollow dies.

Mechanics of Loading for Electroplated Cubic Boron Nitride (CBN) Wheels During Grinding of a Nickel-Based Superalloy in Water-Based Lubricating Fluids

The mechanics of wheel loading of the nickel-based superalloy onto electroplated CBN wheels during grinding with water-based lubricants is proposed. Wheel loading was the primary cause for the significant decrease in grinding wheel life for the current formulation of water-based lubricants tested. Evidence of the specific sequence in the deposition process has been captured through extended evaluation and characterization of the grinding wheel surface and adherent alloy material. The proposed mechanism provides a phenomenological understanding of wheel loading for grinding operations using water-based lubricants, aiming to promote testing of future generation grinding lubricants and advanced fluid delivery methods specific to these operations.