In industries such as aerospace, petrochemistry and automobile, many parts of different machines are under environment which shows high temperature and high pressure, and have their proneness to wear and corrosion. Therefore, the wear resistibility and stability under high temperature need to be further improved. Nowadays, Laser cladding (LC) is widely used in machine parts repairing and functional coating due to its advantages such as lower dilution rate, small heat-affected zone and good metallurgical bonding between coating and substrate. In this paper, LC is introduced in detail from aspects of process simulation, monitoring and parameter optimization. At the same time, the paper gives a comprehensive review over LC material system as high entropy alloys (HEAs), amorphous alloy and single crystal alloy have been gradually showing their advantages over traditional metal materials in LC. In addition, the applications of LC in functional coatings and in maintenance of machine parts are also outlined. Also, the existing problems and the development trend of LC is discussed then.

Recent research and development status of laser cladding: A review

Fatigue crack growth of a railway wheel

The service life of rails would be remarkably reduced owing to the increase of axle load, which can induce the occurrence of damages such as cracks, collapse, fat edges, etc Laser cladding, which can enhance the mechanical properties of the rail by creating a coating, has received great attention in the area of the rails due to the attractive advantages such as low input heat, small heat-affected zone, and small deformation In this paper, recent developments in the microstructural characteristics and mechanical properties of a cladded layer on the rail are reviewed The method of process optimization for enhancing the properties of a cladded layer are discussed Finally, the trend of future development is forecasted

https://www.mdpi.com/2072-666X/12/2/152/pdf

A Review on Microstructural Features and Mechanical Properties of Wheels/Rails Cladded by Laser Cladding

The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime, which hinders the lightweight design of modern railway vehicles. In this study, to ensure the reliability and durability of a brake unit bracket, an attempt was made to integrate the nominal stress method and an advanced damage tolerance method. First, a complex bogie frame was modelled using solid elements instead of plate and beam elements. A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan–Guangzhou high-speed railway line. Based on the probability of foreign damage, a semi-elliptical surface crack was then assumed for residual life assessment. The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years. Moreover, even if a 2-mm depth crack exists, the brake unit bracket can be safely operated for more than 2.27 years, with the hope that the crack can be detected in subsequent maintenance procedures. Finally, an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.

/pdf/damage-tolerance-assessment-of-a-brake-unit-bracket-for-high-3a66ywx64m.pdf

Damage Tolerance Assessment of a Brake Unit Bracket for High-Speed Railway Welded Bogie Frames

Effects of nano-CeO2 on microstructure and properties of Ni625 alloy prepared by laser cladding

Laser cladding has been applied to reduce the wear on rails in a curved track. It is important to evaluate the wear and rolling contact fatigue (RCF) characteristics of laser cladding rails. This paper evaluated the wear characteristics of three types of laser cladding, i.e., Stellite 21, Inconel 625, and Hastelloy-C. The wear of Stellite 21 was reduced by 83% as compared to the untreated rail specimen, while those of Inconel 625 and Hastelloy C were decreased by 42% and 29%, respectively. Meanwhile, when laser cladding is applied, a cladding boundary between the rail and the laser cladding is created. The cladding boundary consists of the rail base material, the heat-affected zone, and laser cladding. At the cladding boundary, various types of microstructures are distributed, and as a result the hardness changes. The wear and RCF characteristics of the cladding boundary caused by rolling contact loads have been evaluated through twin-disc tests. Since Stellite 21 has low hardness at the cladding boundary, it suffered the most severe wear and damages in three types of laser cladding. If laser cladding is applied to reduce the wear of the curved track, the damage of the boundary, as opposed to the wear characteristics, should be taken into consideration. In this paper, Stellite 21 exhibits the best wear characteristics, but Hastelloy C is found to be the most appropriate when simultaneously considering both the wear and RCF of the cladding boundary.

Effects of Laser Cladding for Repairing and Improving Wear of Rails

Fatigue crack analysis in a bolster of a metro train

There is a large interest to find reliable and automatic methods for crack detection and quantification in the railway bogie frame. The non-destructive inspection of railway bogie frame has been performed by ultrasonic and magnetic particle testing in general inspection. The magnetic particle method has been utilized in the defect inspection of the bogie frame but the grinding process is required before inspection and the dust is developed resulting from the processing. The objective of this paper is to apply the inspection method of bogie frame using infra-red thermography. The infra-red thermography system using the excitation of eddy current was performed for the defect evaluation of weld specimen inserted artificial defects. The result shows that the infra-red thermography method can detect the surface and inner defects in weld specimen for bogie frame.

Defect Evaluation for Weld Specimen of Bogie Using Infrared Thermography

The reduction unit is one of the most important components for railway vehicles because the torque of the motor must be transmitted to the wheels of the vehicle by the reduction unit. The faults in the reduction units of high-speed trains are caused by damage such as gear, fatigue. These have serious impacts on safety of the train during operation. To address this development of a system for monitoring, fault diagnosis of the reduction unit is needed to keep the vehicle running safely. Before that can be accomplished, it is most important to understand the vibration characteristics of the reduction unit in a normal state. Vibration diagnosis technology using characteristic-analysis of vibration waveform and frequency is known to be the most effective method for fault diagnosis. In this paper, we analyzed the vibration characteristics of the reduction units two Korean high-speed trains (KTX and KTX II), under normal conditions, by two test methods (driving gear test, full-vehicle test).

Fault Diagnosis of a High-speed Railway Reduction Unit Using Analysis of Vibration Characteristics

The gear-reduction units of Korean high-speed trains consist of a motor reduction unit, an axle gear box reduction unit, and a tripod joint shaft. A reduction gear unit is a gearbox used to reduce the rotational speed of the input shaft to a slower rotational speed on the output shaft. This reduction in output speed helps to increase torque. Defective reduction gear units in high-speed trains are caused by damage to the gear or by gear fatigue. To diagnose potential problems, it is important to know the vibration characteristics of the reduction gear units. In this study, we analyzed the vibration characteristics of reduction gears under various conditions. The test setup included a full-scale test rig to evaluate reduction gear under both normal and extreme operating conditions.

Analysis on the Vibration Characteristics of Reduction Gear Units for High-speed Trains

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