Osman Sahin

Indentation Size Effect and Microhardness Study of β-Sn Single Crystals

The load dependence of apparent microhardness of ?-Sn single crystals having different growth directions is investigated. The measurements are performed on (110) planes of these crystals in the load range from 10 to 50?mN. It is found that the degree of the microhardness anisotropy decreases for higher indentation test loads. The examined materials exhibit the behaviour of indentation size effect (ISE), i.e., the apparent hardness increases with decreasing indentation load. Neither Meyers law nor the proportional specimen resistance (PSR) model can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to modified the PSR model based on the consideration of the effect of machining-induced residually stressed surface on the hardness measurement.

Analysis of load-penetration depth data using Oliver–Pharr and Cheng–Cheng methods of SiAlON–ZrO2 ceramics

Depth sensing indentation tests were carried out to obtain load–penetration depth curves of SiAlON–ZrO2 ceramics under different peak loads ranging from 200 to 1800 mN. The values of indentation hardness (HOP, HCC) and reduced elastic modulus (EOP, ECC) were calculated by using Oliver–Pharr (OP) and Cheng–Cheng (CC) methods. The experimental results revealed that the indentation hardness and reduced elastic modulus exhibit peak-load dependence, i.e. indentation size effect. Both indentation hardness and reduced elastic modulus values were obtained by considering indenter tip roundness and machine compliance. These values obtained from the OP method are higher than from the CC method. On the other hand, hf/hm ratios were used to clarify the indentation deformation behaviour of the SiAlON–ZrO2 ceramic. The experimental hf/hm values were lower than the reported critical value (0.7) for all applied test loads, which is attributed to work-hardening behaviour of SiAlON–ZrO2 composites.

Effect of Carbon Content on the Mechanical Properties of Medium Carbon Steels

The mechanical properties of medium-carbon steels with a carbon content ranging from 0.30 to 0.55 wt.% were investigated by tensile and microhardness tests at room temperature. It was observed that the higher carbon content results in an increase in yield stress and ultimate tensile stress, while the elongation remains essentially constant. The results were explained by the hindering of dislocation motion associated with solid solution hardening

Mechanical Properties of Boronized Fe-0.94%Mn Binary Alloy

Fe-0.94%Mn alloys were boronized at 1210 K during 4 h by the powder pack method. Three distinct regions of cross-sections were found in such alloys. The boride layers were characterized by means of microscopy in terms of coating morphology and thickness. The hardness and thickness of the boride layers were measured, and it was observed that they depend strongly on the thermal processes performed before boronizing the alloys.

Creep Behaviour of Fe–Mn Binary Alloys

Tensile creep behaviour of fine-grained Fe–Mn binary alloys containing 0.42–1.21 wt.% Mn has been investigated in the temperature range from room temperature to 475 K under 10–50 MPa. Tensile tests are carried out with a constant cross-head speed under uniaxial load at a strain rate 10−4s−1. Stress exponent and activation energy are determined to clarify deformation mechanism. The obtained variation of steady state creep rate with respect to the applied stress for Fe–Mn binary alloys exhibits two distinct regimes at about 20 MPa, indicating a possible change in creep mechanism. The average stress exponent is approximately 2.2, which is a characteristic of grain boundary sliding in the alloys. The activation energy for plastic flow varies from 135 to 92 kJ/mol, depending on the Mn content.

Specimen Geometry Effect on the Mechanical Properties of AISI 1040 Steel

The specimen geometry effect on some mechanical properties, such as tensile behaviour and hardness, of borided and unborided AISI 1040 steels was investigated. Boronizing of steels was performed by the powder pack method at 1210 K for 4 h. The specimen geometry and the boride layer thickness and hardness is similar for all tested boronized steels and independent of varying the shape of cross-sections. On the other hand, the ultimate tensile stress and elongation depend on the specimen geometry due to stress concentration at the corners of the specimen.

Effect of Indentation on I-V Characteristics of Au/n-GaAs Schottky Barrier Diodes

Au/n-GaAs Schottky barrier diodes (SBDs) have been fabricated. The effect of indentation on Schottky diode parameters such as Schottky barrier height (φb) and ideality factor (n) was studied by current-voltage (I-V) measurements. The method used for indentation was the Vickers microhardness test at room temperature. The experimental results showed that the I-V characteristics move to lower currents due to an increase of φb with increasing indentation weight, while contacts showed a nonideal diode behaviour.