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In order to investigate the effects of new surface modification method “Laser quenching after coating” on the rolling contact fatigue strength of ceramic coated steel, CrAlN coated specimens were processed by this method under various laser power conditions, and the thrust type rolling contact fatigue tests were carried out for these specimens. The delamination initiation life of CrAlN coated specimen increased with the laser power, however the excessive laser power decreased the delamination initiation life. The adhesive strength of CrAlN coated specimen showed similar variation for the increase of the laser power. The film hardness was almost constant for the increase of the laser power, however the excessive laser power also decreased the film hardness. From these results, it was considered that the increase of the delamination initiation life of CrAlN coated specimen was caused by the increase of the adhesive strength, and the decrease of the delamination initiation life at high laser power was affected by the decrease of the adhesive strength and/or the film hardness.

In order to investigate the effects of a new surface modification method, ‘the substrate quenching after coating’ on the rolling contact fatigue strength, TiN coated steel specimens and CrAlN coated steel specimens were processed by this method and the thrust type rolling contact fatigue tests were carried out for these specimens. In the process of the substrate quenching after coating, two types of quenching methods, furnace quenching and laser quenching, were used.For the furnace quenched specimens, the delamination initiation life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidisation of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the delamination initiation life of the laser quenched specimens was longer than that of the furnace quenched specimens. After the initiation, the delamination of the furnace quenched specimen grew much faster than that of laser quenched specimen. These...

A new surface modification method “laser quenching after coating” using a high power diode laser equipped with a 2dimensional galvano-scanner unit was developed to process a larger area of ceramic coated steel uniformly and efficiently. The laser irradiation tests for 3 kinds of ceramic-coated steels: CrAlN, TiAlN and CrN, were carried out with the scanning laser, and the appropriate irradiation conditions to achieve the uniformly quenched substrate without any surface damage were clarified for these ceramic-coated steels. The area of the substrate surface wider than the laser spot size could be easily quenched by the scanning laser. The adhesive strength, the film hardness of the laser-irradiated regions and the deformation caused by laser irradiation were evaluated. Laser quenching with the scanning laser can effectively improve the adhesive strength and substrate hardness without any detrimental effect on the film hardness of the ceramic-coated specimens. In the deformation of the laserirradiated specimens, two features were recognized; one is the bending, and the other is the expansion of laser-irradiated part. It was found that the deformation of ceramic-coated steel by laser irradiation under the same heat input condition does not depend on the kind of ceramic thin film but on the steel type of the substrate. It was concluded that “laser quenching after coating” with scanning laser could easily improve the adhesive strength and substrate hardness without any detrimental effect on the film hardness of large surface areas in the tested all types of ceramic-coated specimens. Copyright © 2014 VBRI press.

In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness. In the present research, in order to quench a larger area of ceramic coated steel uniformly and efficiently, a high power diode laser equipped with a galvano-scanner was used in the laser heat treatment process. The scanning laser irradiation conditions to achieve uniformly quenched substrates without any surface damage were investigated for three kinds of ceramic coated steels: CrAlN, TiAlN and CrN. The film hardness and adhesive strength of the laser irradiated regions were evaluated. It is shown that scanning laser quenching after coating effectively improved the mechanical properties for larger area of ceramic coated steels.

In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible t...

In order to identify the mechanisms of changes in the magnetic flux density distribution around fatigue cracks that occur during crack propagation, JIS SCM440 specimens were fatigue tested, and the relation between crack morphology and magnetic flux density distribution was investigated. Two features were observed: a high intensity area around the crack tip, and a low intensity area around the crack root. The low intensity area grew larger for wide open cracks and disappeared when the crack was closed by external force. It was hence found that the magnetic flux density distribution is strongly affected by the crack opening.

Introduction It is difficult to make a definite diagnosis of a cracked tooth solely based on an inspection within the root canal, especially in case of microcracks. At present, there seems to be no established method to detect dentinal microcracks in roots; therefore, the current detection techniques need to be improved. Vibrothermography (VibroIR) helps to detect microcracks by the friction heat generated from ultrasonic vibration. The purpose of this study was to establish a novel method using VibroIR to detect dentinal microcracks. Methods The root canals of 20 roots with cracks and control roots were prepared after removing the tooth crowns. A tapered indenter was inserted into the root canal and pressed until a microcrack was created under an optical microscope. Using VibroIR, the detection trials for dentinal microcracks were performed with an ultrasonic vibration power ranging from 0.43 to 1.48 W at an angle of 0°, 30°, 45°, 60°, and 90° between the ultrasonic vibration point and the microcrack line. After the detection test, the microcrack width was measured with an optical microscope. Results Frictional heat was detected in the microcracks with thermography at 0.89 to 1.48 W and at an ultrasonic vibration point angle less than 60° from the crack line for 10 seconds. Microcracks with a width of 4 to 35.5 μm were detected with this method. Conclusions VibroIR may be an effective method for the diagnosis of root dentinal microcracks.

In our previous study, it has been shown that improvement of the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness can be achieved by applying laser quenching. In the present research, in order to demonstrate further development of this method, the fracture strength of laser-irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat-induced changes in the substrate hardness, a cemented carbide WC-Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. Laser quenching has been shown to effectively reduce the fracture strength loss of the ceramic thin films in coated steels.

A new remote nondestructive evaluation technique based on thermoelastic temperature measurement by infrared thermography was developed for the evaluation of fatigue cracks propagating from welded joints in steel bridges. Fatigue cracks were detected from localized thermoelastic temperature changes at crack tips due to stress singularities generated by wheel loading from traffic on a bridge. A self-reference lock-in data-processing technique was developed to improve the signal-to-noise ratio of the thermal images obtained in the crack detection process. Thermoelastic stress analyses in the vicinity of crack tips were carried out after the crack detection process by self-reference lock-in thermography. The stress distribution under wheel loading by traffic was measured by infrared thermography. Stress intensity factors were directly evaluated from the measured stress distribution. It was found that these fracture mechanics parameters can be evaluated with reasonable accuracy by the proposed technique, enabl...

Thermoelastic stress analysis (TSA) using by infrared thermography has been widely used as an effective full-field stress measurement technique. The present authors applied TSA technique to nondestructive evaluation of fatigue cracks in steel bridges, in which fatigue cracks were detected based on singular stress fields observed around crack tips and structural integrity was evaluated based on stress intensity factor calculated from observed near tip stress field. In this paper, a new approach for evaluating stress intensity factor based on TSA technique is proposed. The coefficients including stress intensity factor in the near tip stress field function expressed in higher order terms are determined by the least square fitting using experimentally obtained data by TSA. It was found that values of stress intensity factors K I and K II were obtained in good accuracy.