Study on the Doping Effect Cr-doped Fe Metal Powder and Sintering Temperature on Microstructure and Mechanical Properties of Spur Gear Fabricated by Powder Metallurgy

Abstract

We fabricated mechanical parts of the automotive machines by using Cr-doped the Fe metal powder. We used water as a binder and used a mechanical press for compaction of about 20 ton/in² followed by non-reactive sintering at 1100 ^oC. Cr doped Fe metal powder was prepared in the form of GC with percentage values of 0, 0.5, 1.0, 1.5, and 2.0%. The Cr element has been successfully distributed into the main ferrite or Fe phase. However, there is a difference when the Cr percentage is 2%, it is possible that saturation will occur which results in the accumulation of Cr powder so that a new phase is formed which gives rise to new granules. We can confirm that there is a certain limit in the addition of the element Cr in the manufacture of gears made from Fe powder. Based on the calculation, the average number of the Vickers microhardness as a function of Cr content of 0, 0.5, 1, 1.5, and 2% respectively were estimated at about 131, 184, 291, 302, and 270 HV/0.01, respectively. Furthermore, four samples with different sintering temperatures were prepared for comparative purposes. The shrinkage ratio of the GC after sintering at 900, 1000, 1100, and 1200 ^oC was estimated to be 4.3, 5.7, 7.6, and 9.4%, respectively. The shrinkage ratio of the GC increased linearly when the sintering temperature increased. Sintering temperature variations produce differences in the microstructure of each sample. With the increase of the sintering temperatures, the grains will reach a permanent bond because the constituent particles are fully agglomerate. As a result, grain boundaries between particles will decrease causing the dimensions of the product to shrink so that its density increases. Theoretically, the density value is inversely proportional to porosity. The higher the density value of a product, the lower the porosity value. Increasing the sintering temperature could lead to the appearance of a liquid and the healing of pores. The hardness value and the shrinkage ratio increased with the sintering temperature increased from 900 to 1200 ^oC. The hardness value increased from 297 to 305 HV/0.01, as the sintering temperature increased from 900 to 1200 ^oC.