Development of energy intensive multifunction cavitation technology and its application to the surface modification of the Ni-based columnar crystal superalloy CM186LC.

The present work demonstrates a technique for the hot forging of metal surfaces in water at 1000 °C or higher, termed energy-intensive multifunctional cavitation (EI-MFC). In this process, the energy of cavitation bubbles is maximized, following which these bubbles collide with the metal surface. This technique will be employed to improve the surface structure of CM186LC/DS, a Ni-based columnar crystalline superalloy used to manufacture the rotor blades of jet engines and gas turbines that are exposed to high-temperature oxidizing environments, with the aim of improving creep strength.

Sonoluminescence from ultra-high temperature and pressure cavitation produced by a narrow water jet.

This work developed a small-scale processing apparatus for ultra-high temperature and ultra-high-pressure cavitation (UTPC) incorporating a small diameter (0.1 mm) water jet nozzle. This instrumentation comprised a swirl flow nozzle (SFN) installed on the water jet nozzle so as to obtain UTPC from a multifunction cavitation (MFC) setup.

Rapid Nitriding of Titanium Alloy with Fine Grains at Room Temperature.

Multifunctional surfaces are required to design safe engineering products for human lives. Heating in a nitrogen atmosphere (nitriding) improves the tribological properties but reduces the strength of titanium (Ti) alloys owing to grain coarsening. A rapid nitriding method for Ti alloys forms the nitrided layer on the surface of a Ti alloy by bombarding with commercially pure Ti fine particles with a nitrided phase at room temperature within a short period.

High-temperature corrosion behavior of high-temperature and high-pressure cavitation processed Cr-Mo steel surface.

In this paper, long-term high-temperature corrosion at 500 °C and high-temperature corrosion at the melting temperature of a corrosive ash mixture were examined because the use of high-temperature equipment such as boilers and gas turbines increases year over year. To investigate the optimum cavitation processing conditions for the specimens used in high-temperature corrosion tests, the surface properties of each processed specimen were examined. In specimens processed using multifunction cavitation (MFC), the compressive residual stress was high when the processing time was 10 min and the Cr content on the surface was greater than on the surface of an unprocessed specimen.

Thermal Stress Relaxation and High-Temperature Corrosion of Cr-Mo Steel Processed Using Multifunction Cavitation.

This research investigated high-temperature corrosion (500 °C) of Cr-Mo steel processed using water jet peening or multifunction cavitation (MFC), and the suitability of such steel for high-temperature boilers and reaction vessels. High-temperature corrosion was induced using an embedment test and a coating test using sulfide-type K₂SO₄-Na₂SO₄ powder. To measure the relaxation of the residual stress due to the decrease in work hardening caused by an increase in specimen temperature and the difference in thermal shrinkage between the surface and interior of the specimen, a thermal cycling test was conducted.

Sustainability of compressive residual stress on the processing time of water jet peening using ultrasonic power.

Water jet peening (WJP) is used as a stress improvement method and a countermeasure against stress corrosion cracking (SCC) in the internal structures of reactors in nuclear power plants. However, when residual stress is converted to compressive stress and applied to the specimen surface as a countermeasure against SCC, voids and cracks can easily form inside the specimen because of the increase in the pressure applied to the surface during WJP processing. Recently, multifunction cavitation (MFC), which is WJP using ultrasonic power, has been developed as an alternative to WJP.