Influence of Material Coating on Stress Measurement by Ultrasonic Surface Wave (Part 1)

Ultrasonic surface wave have been implemented to measure or predict the existing stress on material. Surface wave velocity shows linearly increase with stress applied in material. However, various applications were coated their surfaces with high corrode resistance material for example paint or aluminum thermal sprays. It may cause the change of the velocity of surface wave and lead to miss prediction. This paper presents the effect of material coating on surface wave velocity and its attenuations. Paint and Aluminum thermal spray coated on low carbon steel graded S420 (EN 10025 Standard) in the range of 100-500 micron. Through transmission ultrasonic surface wave was applied to measure the velocities change. Their frequencies are 2.25 and 5 MHz respectively. It was found that coating thickness show effect on sound velocity and sound wave attenuation. The benefit is to know the effect of coating and to approve the accuracy of stress measurement by ultrasonic wave.

Plasma Processing of Advanced Materials

A plasma, commonly referred to as the “fourth state of matter,” is an ensemble of randomly moving charged particles with a sufficient particle density to remain, on average, electrically neutral. While their scientific study dates from the 19th century, plasmas are ubiquitous, comprising more than 99% of the known material universe. The term “plasma” was first coined in the 1920s by Irving Langmuir at the General Electric Company after the vague resemblance of a filamented glow discharge to a biological plasma.Plasmas are studied for many reasons. Physicists analyze the collective dynamics of ions and electron ensembles, utilizing principals of classical electromagnetics, and fluid and statistical mechanics, to better understand astrophysical, solar, and ionospheric phenomenon, and in applied problems such as thermonuclear fusion. Electrical engineers use plasmas to develop efficient lighting, and high-power electrical switchgear, and for magneto-hydrodynamic (MHD) power conversion. Aerospace engineers apply plasmas for attitude adjustment and electric propulsion of satellites. Chemists, chemical engineers, and materials scientists routinely use plasmas in reactive ion etching and sputter deposition. These methods are commonplace in microelec tronics since they allow synthesis of complex material structures with submicron feature sizes. A substantial portion of the multi-billion-dollar market for tooling used to manufacture semiconductors employs some form of plasma process. When compared with traditional wet-chemistry techniques, these dry processes result in minimal waste generation. Plasmas are also useful in bulk processing—for example as thermal sprays for melting materials.While the quest for controlled thermonuclear fusion dominated much of plasma research in the 1960s and 1970s, in the last 20 years it has been the application of plasmas to materials processing that has provided new challenges for many plasma practitioners. It is not surprising that the guest editors and several of the authors for this issue of MRS Bulletin come from a fusion plasma-physics background.

New Machining Method for Nickel Based Thermal Sprays

The routine overhaul and repair of gas turbine components requires dimensional restoration of many components. This process is usually accomplished by using various thermal sprays to build up the worn part surface and then machining or grinding the thermal sprays to correct part tolerances and dimensions. These surfaces usually contain numerous holes that generate heavily interrupted surfaces to be machined. The combination of interrupted cuts and a very wear resistant thermal spray causes rapid tool wear on conventional carbide cutting tools. This rapid tool wear also produces poor surface finish, part taper, chipping around the hole edges, and increased tool pressure that could result in lifting or peeling of the sprayed material from the parent metal. This paper summarizes the results of machining nickel based thermal sprays with polycrystalline cubic boron nitride (PCBN) cutting tools. The tests have shown a minimum 2–5x improvement in surface finish, dimensional control, part taper and up to 10x increase in productivity. The PCBN tools also generated lower cutting forces resulting in reduced stress and higher bond strengths in the part. This paper presents the data collected and the recommended machining parameters developed under controlled conditions for machining air plasma sprayed Metco 443, Metco 450, Inconel 718, two wire arc applied TAFA 75B, TAFA 73MXC, and high velocity oxygen fuel applied Inconel 718.