International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Iron powder metallurgy is a method that is widely used in production of steel parts that are utilized as machine components or as parts in automotive industry. Milling is extensively used in powder metallurgy of iron, for purposes of mixing. The hardness and yield strength of milled iron powders increase due to work hardening. This leads to low green density of the cold pressed green parts, prior to sintering. In powder metallurgy, warm compaction is utilized for enhancing the green density and green strength.
In the present study, effect of warm compaction of milled iron powders was investigated. For warm compaction of iron powders, 600 MPa pressure was applied in a steel die at 150 oC. The microstructure of the milled samples was examined by scanning electron microscopy. Hardness values of the cold pressed and warm compacted samples were determined by a Brinell hardness tester. Bending strength values of the samples were determined by a universal testing machine. It was found that the hardness of the cold compacted green samples increased considerably, from about 40 Brinell10 to about 140 Brinell10, as a result of warm compaction. Bending strength values increased to over 100 MPa after warm compaction; whereas the bending strength of the cold compacted green samples were in 10-20 MPa range.

As a relatively new class of materials that exhibits a gradual compositional or microstructural change along one axis, functionally graded materials (FGM) emerged. As a result of this change, properties of the material also vary. This property change can be controlled by tailoring the composition or microstructure of the individual stacks in the FGM.
In the present study, aluminum matrix functionally graded composite materials with increasing amounts of B4C particles in an aluminum matrix were formed. The functionally graded materials were composed of 4 composite stacks with different compositions; namely, 0, 10, 20 and 30 volume % B4C particles. The matrix material was aluminum – 4 wt.% copper alloy. Preparation of the functionally graded materials was conducted through powder metallurgical methods including mixing, cold pressing and sintering without pressure. Samples were produced in dimensions according to 3-point bending standards.
Microstructure of the functionally graded materials contained some porosity, amount of which was seen to increase with increasing B4C reinforcement amount. All the stacks were subjected to Vickers microhardness measurements and it was seen that the hardness of the layers increased significantly with increasing reinforcement amount. The unreinforced layer had a hardness of 55 HV0.1 and that of the layer containing 30 % B4C was 143 HV0.1. On the other hand, the bending strength of the functionally graded material was seen to be lower than that of the unreinforced sample.

Titanium diboride reinforced iron matrix composites were produced via powder metallurgy techniques. Iron powder (<10 microns) and titanium diboride powder (<10 microns) were mixed in a ball mill and the powder mixture was cold compacted in a steel die at 550 MPa pressure. Amount of titanium diboride that was added into iron was in 3-10 wt %. Sintering was performed at 1120 oC for 30 minutes in argon atmosphere. Sintered samples were subjected to three-point bending tests, hardness measurements and microstructural examinations.
It was found that the hardness of the composites increases significantly with the increase in the amount of titanium diboride addition. Hardness of unreinforced iron was 50 Brinell 10 and that of 10 % titanium diboride reinforced composite increased to 100 Brinell 10. On the other hand, there was a decrease in the bending strength and strain of the composites, with increasing titanium diboride addition. Bending strength of unreinforced iron was 850 MPa and that of 10 % titanium diboride reinforced composite decreased to 350 MPa.

Formation of ZrB2-AlN mixed powder by self-propagating high-temperature synthesis (SHS) was investigated. Powders of Zr, B, BN and Al (purity >99 %) was used as the starting materials. Two initial mixtures were prepared and mixed at specific ratios. The first mixture was made of Zr and B, which were weighed at stoichiometric amounts to form ZrB2. The second mixture contained Zr, BN and Al; amounts of which were calculated so as to form ZrB2 and AlN.
The starting powders were mixed in a mortar and pestle, and then the reactant mixture was slightly pressed in a steel die. The SHS reactions were conducted in high purity argon atmosphere, in an SHS chamber. The reactant pellet was ignited from one end with a tungsten wire. The reaction products were examined with scanning electron microscopy and they were subjected to X-ray diffraction analyses.
It was found that when the reactants contained 40 % mixture-1 and 60 % mixture-2, according to the XRD results of the products, the peaks related to ZrB2 were dominant. The product contained some AlN and ZrN. When the amount of mixture-2 was increased to 90 %, the amounts of AlN and ZrN both were observed to increase. When Al amount in mixture-2 was increased by 30 % and mixture-2 was added as 90% into mixture-1, amount of AlN in the reaction products increased and amount of ZrN decreased. According to SEM examinations, ZrB2 particles were seen to be mixed with AlN particles in the reaction products. Size of ZrB2 particles were about 1 micron and AlN particles were larger.

Zamak 3 is a zinc-aluminum alloy with a composition of 3.7-4.3 %Al, <0.05 % Cu, 0.02-0.06 % Mg, rest is Zn. It is well suited for pressure die casting and it results in sufficient mechanical properties and a good surface finish. Zamak 3 is utilized in applications automotive industry, household appliances, in structural applications of buildings, etc. It was reported in literatüre that the mechanical properties of the zamak alloys deteriorate in time at room temperature. In the present study, this effect was investigated by artificial aging of zamak 3 alloy.
Zamak 3 samples were produced by cutting and melting of Zamak 3 ingots at 500 oC, and casting into steel molds. Aging experiments were conducted by keeping the Zamak 3 samples in a muffle furnace for 24 h at temperatures of 85 oC, 105 oC and 130 oC. Optical and scanning electron microscopy was employed for investigating the microstructure of the samples. Hardness values of the samples were measured by a Brinell hardness tester. A universal testing machine was used for conduction three point bending tests of the samples. It was found that both hardness and bending strength of Zamak 3 alloy decreased with increasing aging temperature. Hardness and strength values of Zamak 3 were 89 HB10 and 490MPa, respectively. After aging at 130 oC hardness and strength values were found to fall to 75 Brinell 10 and 415 MPa, respectively.

Functionally graded materials (FGM) containing different amounts of B4C particles within 4 layers in an aluminum matrix were produced and characterized. The layers contained B4C particles at amounts of 0, 5, 15 and 25 volume %. In order to form the composite structure, pure aluminum (<10 microns), copper (1 micron) and B4C powders (<10 microns) were utilized. After mixing, functionally graded materials were compacted and shaped in a rectangular cross sectional geometry, having 6.4 mm thickness, 12 mm width and 33 mm length, by cold pressing at 600 MPa pressure. The parts were pressureless sintered at 610 oC for 30 min in high purity nitrogen atmosphere. The properties of the FGM sample were compared with those of the sample which did not contain B4C particles, and which contained 25% B4C particles throughout the whole sample.
Microstructural examinations were performed by an optical microscope. 3- point bending tests were conducted by a universal testing machine. The sample that did not contain B4C particles presented a 3-point bending strength of 380 MPa, whereas the sample that contained 25 % B4C had a bending strength of 140 MPa. The FGM sample had a bending strength of 190 MPa. However, the failure of the FGM sample was composed of steps. The stepwise failure of the FGM sample was due to delamination and fracture of the layers containing 15 and 25 % B4C. Microhardness values of each layer the samples were determined by Vickers micro hardness measurements.