Fe-Cu-C is the leading material in powder metallurgy method due to its liquid phase sintering ability, theoretically above the melting point of copper; 1083 ˚C, strengthening the structure. The sintering temperature is important because it affects the diffusion of copper and carbon into the iron matrix. Therefore, the aim of this project was to study the microstructural evolution and the mechanical properties under different sintering temperatures of mixed iron, copper and carbon (Fe-Cu-C) compacts during liquid phase sintering.
The effect of compaction pressure on the compaction of Fe-Cu-C powder was also discussed in this study. The success and final outcome of this senior year project requires a lot of help and guidance from many people and I am extremely fortunate to have received this during the completion of my senior year project. Mazli Mustapha for his exemplary guidance, monitoring and constant encouragement throughout the last year's project period.
My thanks and appreciation also go to Universiti Teknologi PETRONAS for successfully completing this final year project. This graduation project has given me a lot of experience in working on a research project.
INTRODUCTION
- Background of the Project
- Problem Statements
- Objectives
- Scope of Study
However, powder metallurgical sintered parts usually have residual porosity which affects the mechanical strength and other properties. Furthermore, the resulting microstructure and properties of the Fe-Cu-C press were found to be dependent on the thermal history during the fabrication process. Therefore, the temperature during the sintering of Fe-Cu-C is important to obtain the best result from the sintering.
The objectives of this project are to study the effects of different sintering temperatures on the microstructural evolution and the mechanical properties of mixed iron, copper and carbon powders (Fe-Cu-C) according to the MPIF standard for the FX-2008 composition during sintering in the liquid phase. . This project also studies the effect of compaction pressure on the compaction of Fe-Cu-C powder. This work will present the research performed to study the sintering properties of Fe-Cu-C compact.
In the experiment, the readily available iron, copper, and carbon powders are mixed to the Metal Powder Industry Federation (MPIF) standard of FX2008, which is 79 wt% Fe, 20 wt% Cu, and 1 wt% C. the effect of compaction pressure on the density of the samples will also be discussed.
LITERATURE REVIEW
- Powder Metallurgy Method
- Iron-Copper-Carbon Alloy
- Compressibility of Fe-Cu-C System
- Lubricant
- Liquid Phase Sintering (LPS) Method
- Mechanical Testing Of Materials
- Sintered Density
- Hardness
According to Šalak (2005), alloying with copper not only increases the strength of alloys, but also improves machinability. The compactness of the Fe-Cu-C powder depends on the compressibility of the powder. The term compressibility is a measure of the ability of a powder to deform under applied compression and is also described as the ratio of pressure to density (Anand & Kulkarni, 2013).
Kulkarni (2013) further explains that an increase in compressive load results in an increase in compaction density and after a certain degree of densification, pressure has no effect. As a protective measure to protect the die while pressing the metal powder, a lubricant is applied to the die wall. Thus, the capillary force that pulls the grains together arises from the liquid wetting the solid due to solubility.
At the same time, the thickening of the compounds is supported by the high temperature, which softens the solid. It is measured by pressing the indentation test tip into the surface of the sample.
METHODOLOGY
- Raw Materials
- Iron Powder
- Copper Powder
- Raw Materials Processing
- SEM Analysis
- Weighing and Mixing
- Compaction of Mixed Powders
- Sintering
- Physical Properties Measurements
- Linear Dimension
- Sintered Density
- Microstructure Observation
- Sample Preparation
- Microstructure Observation before Etching
- Microstructure Observation after Etching
- Mechanical Testing
- Vickers Micro Hardness
- Final Year Project Flow Process
- Gantt Chart & Project Activities
- Key Milestones
A lubricant can either be mixed with the metal powder or applied to the surface of the die wall. Lubricant also functions as a binder to keep the shape of the metal powder after compaction. The lubricant was applied to the surface of the die wall before the mixed metal powders were inserted.
The lubricant will compact together with the powders and wet the surface of the compacted powders to hold the shape. Forming samples using the powder metallurgy method begins with the densification of loose powder into a green compact in a solid cavity cover. A high carbon steel material was used to make the cylindrical shape of the green compact.
The die wall and die surface were first coated with zinc stearate before the powders were introduced. The samples were properly arranged on the ceramic crucible and placed in the center of the furnace to ensure uniform heating of the samples. The literature study shows that the higher the compaction pressure, the higher the compaction of the compacts.
Therefore, to study the linear dimensional changes of the samples, we chose the samples compressed at the highest pressure (600 MPa). The diameter of the samples was measured with a vernier caliper in several trials at different points to obtain the average of the diameter. The data were then compared to the original diameter of the die and the percentage of dimensional change was recorded.
The sintered density of the samples was calculated using Equation 2 where 𝜌𝑤 was the density of water at room temperature (0.9997 g/cm3). After the samples were placed in the center of the ram, the ram was lowered until it reached the lowest depth. After the sample is mounted, the surface of the samples must be ground to produce a flat surface.
The surface of the samples was mechanically sanded by hand on a sanding machine with SiC paper under running water. At least 5 indentations were made for each sample and the mean value was obtained and recorded as the microhardness of the samples.
RESULTS AND DISCUSSIONS
- Powder Distribution
- Dimensional Changes and Microstructure Evolution
- Etched condition photomicrograph of sintered Fe-Cu-C . 31
- Compaction Pressure Effect and Microstructure Overview
- Surface Hardness
The dimensions of the samples may change due to the reaction between the elements in the alloy during the sintering process. From the result, the dimensions of the samples were larger than the die size mostly due to growth. The photomicrograph showed the presence of unmelted copper in the structure, further confirming that the growth is mainly due to the diffusion of carbon into the iron matrix.
The presence of the unmelted copper in the compact materials was due to the significantly lower sintering temperature than the melting temperature (1083 ˚C) of copper. A further increase in the sintering temperature to 1080 ˚C caused an increase in linear growth to about 0.85% of the die size. The cross-sectional photograph of the compact materials sintered at 1080 ˚C in Figure 4.4 (c) confirmed the presence of copper (white area) in the structure.
The data for the sintered density of different compaction pressures at different sintering temperatures are summarized in Figure 4.6. The increase in sintered density is due to the increase in the extent of sintering and diffusion of carbon in the iron matrix. The phenomena copper began to melt and dissolve in the iron matrix above the sintering temperature 1080 ˚C has also contributed to the increase in sintered density of the compact.
The compaction pressure also plays a significant role in compaction of the compact as shown in Figure 4.7. While the sintering temperature was maintained at 1200 ˚C, the existence of the pores was clearly visible in the compact compacted at 180 MPa. From the micrographs, it can be clearly seen that as the compaction pressure increases, the porosity level of the samples is reduced.
From the obtained results, a compaction pressure of 600 MPa is required to reduce the presence of pores in the compaction. This increase in hardness was due to the initially compacted structure before sintering, the increase in sintering extent and the diffusion of carbon in the iron matrix. The mechanism of copper starting to melt and dissolve in the iron matrix at a sintering temperature above 1080 ˚C and almost complete bonding also contributed to increasing the hardness of the compact.
CONCLUSIONS AND RECOMMENDATIONS
Conclusion
Compressibility studies of the effect of increasing iron content on copper-iron powder mixtures. ASTM B Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes' Principle", ASTM International, West Conshohocken, PA, 2008, www.astm.org. Effect of copper alloy addition method on the dimensional response of sintered Fe-Cu- C steel.
Area of die
Sintered density of samples
