| Warm compaction is a process capable of fabricating high density, high precision and high performance iron-based powder metallurgy (P/M) materials at low cost. Based on the research development in warm compaction at home and abroad, from macrocosmic and microcosmic angle, by the means of both theoretical analysis and experimental investigation, compaction rules of iron powders at the warm compaction process were systematical and deeply studied. As a result, the densification mechanism of warm compaction was revealed. Further experiments demonstrated the influence of compaction process on both green and sintered properties of iron-based P/M materials and high density tungsten-based alloys, and high-density, high-performance P/M materials were prepared. The warm compaction behaviors of homemade iron powders via die wall lubrication were also studied in present work. Moreover, with respect to the effect degree of various factors in warm compaction process, optimal parameters were proposed to fabricate iron-based P/M materials. The major conclusions of this paper were summarized as following:(1) The lubricants of warm compaction used at home and abroad are all kept secret as patents. A large number of investigations show that common lubricants like zinc stearate, WSA and ME are all applicable to the warm compaction process of iron powders and other powders. At the appropriate warm compaction process of powders with admixed lubricants like zinc stearate and WSA, the green densities of iron powders and Fe-2Cu-0.6C alloy could reach 7.33g/cm~3 and 7.29g/cm~3 at 700MPa, respectively. For 90W-7Ni-3Fe alloy, the green densities reached 11.65 g/cm~3 at 400MPa.(2) The densification process of warm compaction was analyzed, based on a large number of warm compacted experiments. A densification model in powder warm compaction described as C_P=aP/(1+bP)+cexp(-d/P) was originated from Cooper-Eaton, its modified model and Kawakita theory. Densification mechanism of iron powders was analyzed according to the model. Results indicate that particle rearrangement is the primary densification mechanism at relatively low compaction pressures, while the plastic deformation dominates the densification at higher compaction pressures. Particle rearrangement plays a more important role in the whole densification process, compared to plastic deformation.(3) For Fe-Cu-C alloys, powders with admixed different lubricants were compacted at variours temperatures. Experiments results imply that the relationship between compaction pressures and green densities of alloys could all be described by Huang Peiyun equation. The value m in the equation all decreased with the elevation of compaction temperature, and reached the minimum at 110℃for alloy powders with admixed zinc stearate, while at 130℃with admixed WSA. However, for alloy powders with admixed two different lubricants, the value M in the equation all reached the maximum with temperature increasing from room temperature to 110℃. Moreover, both m and M had lower values in powders with WSA than with zinc stearate, except m at 90℃. As a general, alloy powders with admixed two different lubricants all exhibited the best compation behavior when performed at 130℃.(4) The warm compaction behaviors of non-lubricant admixed domestic reduced iron powders WHF80·240 via die wall lubrication were studied in present work, and the resulting evidence indicates that domestic reduced iron powders could also be applied to the warm compaction process. And also, samples of iron powders without admixed internal lubricant have a sintered density 7.19g/cm~3 on average, after single-press/ single-sinter (SP/SS) at 690MPa and 140℃. This offers a practical foundation for extending the application of warm compaction in China and for the cost reduction.(5) With regard to Fe-4Ni-1.5Cu-0.5Mo-0.6C, the major factors such as compaction pressure, compaction temperature and lubrication condition which affect the warm compaction process of iron-based P/M materials were studied by the orthogonal test method. Results show that compaction pressure plays a most important role, then lubricant condition, and then compaction temperature. And it is found by analysis of variance that the influence of compaction pressure on the green density is highly significant, lubricant condition significant, and compaction temperature inapparent. Conditons as 700MPa pressure, die wall lubrication, non-admixed internal lubricant and 140℃temperature are the optimal parameters in warm compaction process of Fe-4Ni-1.5Cu-0.5Mo-0.6C. Moreover, certain military products were manufactured by optimized warm compaction process. The technical performances of products meet the specific requirements and it will bring preferable social and economic benefits.
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