Numerical Interpretation of Hydrogen Thermal Desorption Spectra for Iron with Hydrogen-Enhanced Strain-Induced Vacancies

We obtained thermal desorption spectra of hydrogen for a small-size iron specimen to which strain was applied during charging with hydrogen atoms. In the spectra, a shoulder-shaped peak in the high-temperature side was enhanced compared with the spectra of the specimen to which only strain was applied. We also observed that the peak almost disappeared by aging processes at ≥ 373 K. Then, assuming that the shoulder-shaped peak results from hydrogen atoms released by vacancies, we simulated the thermal desorption spectra using a model incorporating the behavior of vacancies and vacancy clusters. The model considered up to vacancy cluster $${{V_9}}$$ V 9 , which is composed of nine vacancies, and employed the parameters based on atomistic calculations, including the H trapping energy of vacancies and vacancy clusters that we estimated using the molecular static calculation. As a result, we revealed that the model could, on the whole, reproduce the experimental spectra, except two characteristic differences, and also the dependence of the spectra on the aging temperature. By examining the cause of the differences, the possibilities that the diffusion of clusters of $${V_2}$$ V 2 and $${V_3}$$ V 3 is slower than the model and that vacancy clusters are generated by applying strain and H charging concurrently were indicated.

An analytical model for the magnetostriction strain of ferromagnetic materials subjected to multiaxial stress

Magnetostriction is the magnetisation-induced strain in ferromagnetic materials. It highly depends on mechanical stress. Stress state in electromagnetic devices is usually multiaxial and its effect on magnetostrictive properties is not easily predicted. In this paper, an original three-parameter analytical model for the stress-dependent magnetostriction strain of ferromagnetic materials is proposed. It is based on a simplified energetic description of magneto-elastic behaviour. It follows a similar method previously adopted for the description of the effect of stress on the magnetic permeability of magnetic materials. It is applied for the first time to the magnetostriction behaviour and results in a simple formula to express the effect of multiaxial magneto-mechanical loadings on the magnetostriction strain. The approach also naturally includes the description of the so-called ΔE effect. The analytical formula is derived in the paper. It shows very satisfying agreement with experimental results on iron–cobalt alloy and pure iron specimen.

THE PROPERTIES OF CAST IRON SURFACE LAYERS MODIFIED BY LASER ABLATION MICROMACHINING

The article presents the results of model laboratory tests, including the measurement of temperature, friction force, and linear wear of the surface layer of samples made of grey cast iron sliding against a steel counterpart. The surface layer of the cast iron specimen was modified using ablative laser micromachining in order to change its macro- and micro-geometry. To produce regular oil micro-reservoirs in a shape of micro-channels, an Nd: YAG laser (λ = 1064 nm, ƒ = 1 – 100 kHz, E = 50 J, P = 50W) with a special focusing system was used. Comparative studies included a grey cast iron specimen subjected to conventional mechanical machining and a specimen modified by ablative laser micromachining. 41Cr4 steel with a hardness of 50 HRC was used as a counterpart. Tribological tests were run in a pin-on-disk (T-11 tribometer) test set-up. The best results in the reduction of friction, temperature, and wear were obtained for samples with oil micro-reservoirs (made of ablative laser texturing) in a shape of micro-channels covering 5% of the entire tribological contact surface.

Hardness characterisation of grey cast iron and its tribological performance in a contact lubricated with soybean oil

The effect of hardness of grey cast iron flat specimen on its wear and friction on the contact were characterised with the presence of vegetable oil as biolubricant. Prior to the tribological test, the as-received grey cast iron flat specimen hardness was characterised. Friction and wear tests were then conducted using a ball-on-flat reciprocating sliding contact. The one-way analysis of variance (ANOVA) was used to determine the significance of friction and wear data with a 95% significance level. The wear scars after the test were then characterised by surface roughness and wear mechanism. The microstructure and elemental analysis were also reported. The average value of hardness was 210 HV with a large difference between minimum (185 HV) and maximum (250 HV) values. The friction and wear performance of grey cast iron specimens with soybean oil varied with its hardness. The specimens with higher hardness gave lower friction coefficient and greater wear resistance than the lower hardness specimens. The difference in coefficient of friction produced between high hardness specimens (COF = 0.122) and low hardness specimens (COF = 0.140) was 17%. In terms of mass loss, the low hardness specimens (mass loss = 50.38 mg) and the high hardness specimens (mass loss = 12.90 mg) produced a difference of 74%. It is shown that, with soybean oil lubricant, the grey cast iron specimen can produce wide range of tribological data especially on mass loss due to its hardness distribution. The influence of soybean oil lubrication in this work is less in improving the wear resistance (about 7%), but greater for friction reduction (about 24%) compared to an unlubricated grey cast iron surface. The hardness of grey cast iron specimen is an important parameter that needs to be specifically measured and controlled on the contact due to wide hardness distribution of grey cast iron may produce variation in tribological data.

Improvement of Engine Coolant Ultrasonic Cavitation Apparatus

The structure of cast iron specimen and the temperature control unit of the engine coolant ultrasonic cavitation apparatus were improved in this paper. The broken problem of cast iron specimen was solved by split-structure design, which also solved the loose binding problem between specimen and sonotrode. The temperature control unit included a beaker with water circulating jacket, water bath, circulating pump and connection hose. The temperature control unit overcame the difficulty of the temperature control of test coolant solution. More important, the temperature control inside the soundproof box was realized, which avoided the effect of ultrasonic vibration noise on the health of operator. The unit has the characteristics of simple, practical and easy to use.

Correlation between the Grain Orientation Dependence of Color Etching and Chemical Etching

A gray cast iron specimen was investigated by color and chemical etching with optical and atomic force microscopy, and the effect of grain orientation on the effectiveness of etching was examined. It was proven that the grain orientation dependence of chemical and color etching is just the opposite, and that the specimen surface after color etching is not uniformly smooth. Explanation for the layer structure of the color etched iron specimen is given.

Application of Inclined Cooling Plate to Fabrication of Semi-Solid Cast Iron

The influence of angles of inclined cooling plate on cast structure and mechanical properties of cast iron was investigated experimentally in 3.1 wt.% C containing hypoeutectic semisolid cast irons fabricated by flowing the molten melt over the inclined cooling plate and pouring into a preheated permanent mold. The variables used in this study were angles of the cooling plate (5 ~ 15 deg) and the mold temperatures (500~700 deg). The microstructure of resultant specimens were characterized by measuring grain sizes of primary austenite and its solid fraction, using an optical microscope equipped with a digital image analyzer. It was shown that the spherical-like austenite (1.4 aspect ratio) was formed at the cast iron specimens prepared in employing a 10 deg angle of the inclined cooling plate. This was ascribed to the relative extent of duration time of the flowing melt which determine the solidification rate of the melt. The peak hardness and impact values were achieved in the semi-solid cast iron specimen with relatively more spherical austenite. The measured values were approximately 44HRC and 1.71 J/cm2.