N. Ucar

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.

Schottky Barrier Height Dependence on the Metal Work Function for p-type Si Schottky Diodes

We investigated Schottky barrier diodes of 9 metals (Mn, Cd, Al, Bi, Pb, Sn, Sb, Fe, and Ni) having different metal work functions to p-type Si using current-voltage characteristics. Most Schottky contacts show good characteristics with an ideality factor range from 1.057 to 1.831. Based on our measurements for p-type Si, the barrier heights and metal work functions show a linear relationship of current-voltage characteristics at room temperature with a slope (S=ϕb/ϕm) of 0.162, even though the Fermi level is partially pinned. From this linear dependency, the density of interface states was determined to be about 4.5 · 1013 1/eV per cm2, and the average pinning position of the Fermi level as 0.661 eV below the conduction band

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

The Temperature Dependence of Work-Hardening Rate in Invar Fe–Ni Alloys

The stage I work-hardening behavior of Invar Fe-Ni alloys was studied in tension in the temperature range from room temperature to 700 K. Work-hardening rate (WHR) is a function of temperature and has a peak at about 560 K. The anomalous strength is attributed to thermally activated cross-slip.

Effect of Boronizing on Microhardness and Wear Resistance of Steel AISI 1050 and Chilled Cast Iron

Steel AISI 1050 (steel 50) and chilled cast iron are studied after 5-h solid-phase boronizing from a powder environment at 900 °C. The surfaces of the boronized specimens are studied by x-ray and electron microscopic analyses and their Vickers microhardness is measured. The wear resistance is determined by the pin-on-disc method.

Frequency dependence of capacitance of Au/n-GaAs Schottky diode under hydrostatic pressure

Au/n-GaAs Schottky barrier diodes have been fabricated and the characteristics of capacitance versus frequency under hydrostatic pressure and forward bias were investigated. Although the capacitance is independent of frequency over 50 kHz, it was found that the capacitance strongly depends on forward bias and hydrostatic pressure due to a change of ionized defect concentration in the low-frequency region. These pressure-dependent studies may be of importance for the application of this material as a pressure-sensitive capacitor.

The Effect of Boronizing on the Magnetization Behaviour of Low Carbon Microalloyed Steels

The change of saturation magnetization in boronized low carbon microalloyed steels was investigated as a function of boronizing time. Specimens were boronized in an electrical resistance furnace for times ranging from 3 to 9 h at 1123 K. The metallurgical and magnetic properties of the specimens were investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). A boride layer with saw-tooth morphology consisting of FeB and Fe2B was observed on the surface, its thickness ranged from 63 µm to 140 µm depending on the boronizing time. XRD confirmed the presence of Fe2B and FeB on the surface. The saturation magnetization decreased with increasing boronizing time. This decrease was attributed to the increased thickness of the FeB and Fe2B phases. Cracks were observed at the FeB/Fe2B interfaces of the samples. The number of interfacial cracks increased with increasing boronizing time.

Time Dependence of Current-Voltage Characteristics of Pb=p-Si Schottky Diode under Hydrostatic Pressure

Abstract The effect of time on the characteristic parameters of Pb/p-Si Schottky diodes has been presented as a function of hydrostatic pressure. Current-voltage curves of the Pb=p-Si Schottky diodes have been measured at immediate, 15, 30, 60, and 120 min intervals under 1, 2, and 4 kbar hydrostatic pressure. It has been found that the values of the ideality factor have been approximately unchanged with increasing time. On the other hand, the barrier height of the Pb=p-Si structure slowly increase with increasing time, while these parameters also change with hydrostatic pressure. The diode shows nonideal current-voltage behaviour with an ideality factor greater than unity that can be ascribed to the interfacial layer and the interface states. In addition, the Schottky barrier height increases with a linear pressure coefficient of 92 meV=kbar, which is higher than the pressure coefficient of the silicon fundamental band gap.

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.