Browsing by Author "Scholtz, Arno Paul"

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    A Study of copper infiltration for conventional ferrous powder metallurgy.
    (Stellenbosch : Stellenbosch University, 2018-12) Scholtz, Arno Paul; Blaine, Deborah; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Powder metallurgy (PM) describes a group of manufacturing technologies whereby fine metallic powders are consolidated to create engineering components. The most widely used PM technology is the press-and-sinter process, used to manufacture ferrous alloys. Ferrous PM is frequently sinter-infiltrated with copper (Cu) in order to improve the materials machinability. During sinter-infiltration, molten copper infiltrates the inherently porous PM structure, filling the pores and creating a more dense, less porous material. Residual Cu, from incomplete infiltration, is a common defect in copper infiltrated PM parts. This project investigates the parameters of sinter-infiltration that are critical to successful infiltration and the production of high-quality Cu infiltrated ferrous PM alloys. Common reasons for poor infiltration include incomplete delubrication prior to sintering, and inadequate furnace atmosphere and temperature control. Both of these aspects can introduce impurities into the material during the sintering process, which inhibits efficient infiltration and sintering. This study focuses specifically on the influence of delubrication and furnace control on the sinter-infiltrated material quality. A proprietary copper-infiltrated ferrous PM alloy, with specified processing parameters, is used for this study. A systematic evaluation of both the delubrication and copper-infiltration processes is presented. In order to perform this evaluation, it was necessary to implement control of the furnace temperature and atmosphere. As such, an extensive overhaul of the furnace at Stellenbosch University, with particular attention given to both the electrical and process gas flow systems, was performed and the details are presented in this study. The results of the study indicate that in order to successfully perform good quality sinter-infiltration of the proprietary alloy with copper, different process gas atmospheres are required in the furnace for the delubrication and sintering steps, respectively. During delubrication, a reducing atmosphere of 80:20 vol% N2:H2 with a dewpoint of 8 °C must be maintained. During sintering an atmosphere composition of 80:20 vol% N2:H2 must be maintained with a low dewpoint of -35 °C. For the cooling of the samples an atmosphere composition of 95:5 vol% N2:H2 was used. Furthermore, a detailed metallographic analysis of the consecutive stages of copper infiltration, over the temperature range of 1070 to 1130 °C was conducted. The results of which show how the interaction between Cu and Mn in the alloy significantly influences the melting and infiltration behaviour. This research provides valuable insight into the high sensitivity of the copper infiltration process to furnace atmosphere control, as well as the advantage of understanding the detailed interaction between different alloying elements in the PM material during copper infiltration. Insight leads to the ability to control the process and to design for good quality copper infiltration during sintering.