Search results

The purpose of this paper is to investigate the morphological and metallurgical changes of laser gas‐assisted nitriding of titanium implants.

Laser gas‐assisted nitriding of titanium implant is carried out and the metallurgical as well as the morphological changes in the nitride layer are examined using optical microscopy, SEM, XRD, and X‐ray photoelectron spectroscopy. Temperature and thermal stress fields are computed during the laser heating process adopting the finite element method. The residual stress formed in the nitride layer is measured using the XRD technique while micro‐indentation tests are carried out to determine the fracture toughness of the surface after the laser treatment process.

It is found that nitride depth layer extends to 40 μm below the surface and it is free from the cracks and micro‐voids. The residual stress formed on the surface region is higher than at some depth below the surface in the nitride layer, provided that the maximum residual stress is less than the elastic limit of the substrate material.

The paper contains original findings and the findings are not submitted any other journal for publication.

Laser bending is a good candidate to replace the flame bending process. The electrochemical response of laser bending region changes due to the microstructural modifications and high level of residual stress developed in the laser‐irradiated region after the bending process. Consequently, investigation into laser bending and microstructural changes in the irradiated region as well as the electrochemical response of bending section becomes essential. This paper aims to focus on the laser bending process.

The laser bending of steel sheets was carried out. The microstructural changes in the bending region are examined using the scanning electron microscopy and X‐ray diffraction. The electrochemical response of the bended sections is investigated through potentiodynamic tests.

It is found that laser‐irradiated surface is free from cracks and cavitations. However, deep pit sites due to secondary pitting are observed in the bending sections.

The experiment is limited to certain thickness of the steel sheets. Increasing workpiece thickness reduces the bend angle. However, introducing high‐intensity laser beams improves the bend angle on the expense of high surface roughness in the bend section.

Laser bending process is involved with non‐mechanical tooling with low cost and precision of operation. Moreover, laser bending is a good candidate to replace the flame bending process. Consequently, laser bending finds application in industry. However, under the corrosive environment care should be taken.

The work presented is original and has not been published anywhere before. The findings will be useful for researchers and engineers working in the sheet metal forming area.

The laser nitriding process is involved with high temperature heating and high cooling rates. This, in turn, results in high levels of thermal stresses in the heated region. Moreover, the residual stress in the heated region remains high after the completion of the heating process, which limits the application of the laser nitriding process. The purpose of this paper is to investigate thermal stresses development and residual stress levels in the nitrided region.

The microstructural changes and residual stress development in the laser gas‐assisted nitrided zone are examined. Finite element modeling is carried out to predict temperature and stress fields in the laser nitrided layer. The indentation tests and X‐ray diffraction (XRD) technique are used to determine the residual stress levels while previously derived analytical formula is used to predict the residual stress levels in the nitrided region.

The residual stress predicted attains values within 230 MPa, which remains almost uniform in the nitrided layer, except in the surface region. In this case, residual stress reduces slightly due to the low temperature gradient developed in this region and the unconstrained expansion of the free surface. When comparing the residual stress predicted with the measurement results as obtained from the XRD technique as well as the indentation tests, all the results are in reasonably good agreement. The small discrepancies between the experimental data and predictions are attributed to the assumptions made in the model study and the measurement errors.

The depth of nitrided layer is limited 60 μm. This limits the applicability of the coating for high wearing rates.

The nitrided surface improves the surface properties of steel, which can be used in industry more efficiently.

The paper describes an original model study on stress formation, an experiment for surface characterization and estimation of residual stress formation and contains new findings.

Despite the vast potential of mobile phone use, grape smallholder farmers’ satisfaction with mobile phone use has attracted insufficient attention among scholars in Tanzania. The study examined factors influencing satisfaction with mobile phone use for accessing agricultural marketing information.

The study used a cross-sectional research design and a mixed research method. Structured questionnaire and focus group discussions were used to collect primary data from 400 sampled grape smallholder farmers. Data were analysed inferentially involving two-way analysis of variance, ordinal logistic regression and thematic analysis.

The findings indicate a statistically significant disparity in grape smallholder farmers’ satisfaction across different types of agricultural marketing information. Grape smallholder farmers exhibited higher satisfaction levels concerning information on selling time compared to all other types of agricultural marketing information (price, buyers, quality and quantity). Factors influencing grape smallholder farmers’ satisfaction with mobile phone use were related to perceived usefulness, ease of use, experience and cost.

This study contributes to scientific knowledge by providing actionable insights for formulating unique strategies for smallholder farmers’ satisfaction with agricultural marketing information.