A Study of copper infiltration for conventional ferrous powder metallurgy.

Scholtz, Arno Paul (2018-12)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Poeiermetallurgie (PM) beskryf ’n groep vervaardigingstegnieke waardeur fyn metaalpoeiers gekonsolideer word om ingenieurskomponente te skep. Die mees gebruikte PM tegnologie is die pers-en-sinter proses, wat gebruik word om ysterhoudende allooie te vervaardig. Ferro PM is dikwels sinter-geïnfiltreer met koper (Cu) om die materiaal se bewerkbaarheid te verbeter. Tydens sinter- infiltrasie infiltreer gesmelte koper die inherente poreuse PM struktuur, vul die porieë en skep ’n digter, minder poreuse materiaal. Residuele Cu, van onvolledige infiltrasie, is ’n algemene probleem in koper geïnfiltreerde PM dele. Hierdie projek ondersoek die parameters van sinter-infiltrasie wat krities is vir suksesvolle infiltrasie en die produksie van hoëgehalte Cu-geïnfiltreerde ferro- PM-legerings. Gewone redes vir swak infiltrasie sluit onvolledige delubrikasie voor sintering, en onvoldoende oond atmosfeer en temperatuur beheer. Albei hierdie aspekte kan onreinhede in die materiaal tydens die sinterproses skep, wat effektiewe infiltrasie en sintering inhibeer. Hierdie studie fokus spesifiek op die invloed van delubrikasie en oond beheer op die sinter-geïnfiltreerde materiaal kwaliteit. ’n Besitlike koper-geïnfiltreerde Ferro PM-legering, met gespesifiseerde verwerkingsparameters, word vir hierdie studie gebruik. ’n Sistematiese evaluering van beide die delubrikasie- en koperinfiltrasieprosesse word aangebied. Ten einde hierdie evaluering te kan uitvoer, was dit nodig om beheer oor die oondtemperatuur en atmosfeer te implementeer. ’n Omvattende opknapping van die oond aan die Universiteit Stellenbosch, met besondere aandag aan beide die elektriese en prosesgasvloeistelsels, was uitgevoer en die besonderhede word in hierdie studie aangebied. Die resultate van die studie dui daarop dat ten einde suksesvolle sintere-infiltrasie van die besitlike allooi met koper te kan uitvoer, word verskillende prosesgas-atmosfere in die oond vir die delubrikasie en sinteringstappe onderskeidelik benodig. Tydens delubrikasie moet ’n reduserende atmosfeer van 80:20 vol % N2:H2 met ’n doupunt van 8 °C behoue bly. Tydens sintering moet ’n atmosfeer samestelling van 80:20 vol% N2:H2 behou word met ’n lae doupunt van minstens -35 °C. Vir die afkoeling van die monsters is ’n atmosfeer samestelling van 95:5 vol% N2:H2 gebruik. Verder is ’n gedetailleerde metallografiese analise van die opeenvolgende stadiums van koperinfiltrasie, oor die temperatuurreeks van 1070 tot 1130 (°)C uitgevoer. Die resultate toon hoe die interaksie tussen Cu en Mn in die allooi die smelt- en infiltrasiegedrag aansienlik beïnvloed. Hierdie navorsing bied waardevolle insig in die hoë sensitiwiteit van die koperinfiltreringsproses om oond-atmosfeerbeheer te gebruik, sowel as die voordeel om die gedetailleerde interaksie tussen verskillende legeringselemente in die PM-materiaal tydens koperinfiltrering te verstaan. Insig lei tot die vermoë om die proses te beheer en te ontwerp vir goeie gehalte koperinfiltrasie tydens sintering.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105089
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