High Strength Powder Metallurgy Materials

The main factors controlling the mechanical properties and dimensional stability of sintered iron base alloys are discussed in detail in the literature review of this thesis. From this, the need to examine in detail the iron-carbon-copper-nickel system is established. In order to clarify the industrial aspects of the project, the review also contains a description of the basic stages in the ferrous powder metallurgy process, and is concluded with a cost analysis containing a detailed breakdown of the costs involved in producing a component by the powder metallurgy route and by machining from bar stock. The experimental work was planned statistically, using a factorial design. The object was to determine the significance of the effect of alloy composition and as-pressed density on the strength and dimensional stability of sintered iron-carbon-copper- nickel alloys, prepared from pre-mixed elemental powders. The magnitude of the significant effects has also been determined using multiple regression analysis. The importance of as-pressed density in determining mechanical properties, is confirmed. A number of main effects and interactions between variables, particularly between alloying elements, appear to have a significant effect on strength and dimensional stability during sintering. The multiple regression equations obtained are complex since they contain a number of interaction terms and the magnitude of the effect of each variable, particularly alloying elements, is highly dependent on the levels of the other variables. A second regression analysis was made using the results obtained from alloys of "commercial significance’. Thus, the highly alloyed materials were excluded on the basis of poor properties and expense. Mechanisms involved in strengthening and dimensional control are briefly discussed to illustrate that there is some agreement between the effects observed from this investigation and those proposed in published literature.