Rex J. Harvey

Effect of MEMS-compatible thin film hard coatings on the erosion resistance of silicon micromachined atomizers

A comparison of five different MEMS-compatible, thin film, hard coatings has been performed using silicon (Si) micromachined atomizers as test devices. Single-crystal and polycrystalline silicon carbide, silicon nitride, silicon dioxide, and diamond-like carbon were either thermally grown or chemically vapor deposited onto the non-planar topography of the device. Eighteen-hour long, industry-standard erosion tests were performed to qualitatively evaluate the coatings for erosion resistance when exposed to an aggressively contaminated test fluid. No wear was measured on the majority of the swirl chamber floor for the five coatings, though varying degrees of erosive wear were observed at the edge of the exit orifice. The single-crystal silicon carbide demonstrated the best wear performance of all the coatings, exhibiting no noticeable changes of its surface morphology as a function of the erosion tests. The silicon nitride and diamond-like carbon coatings showed the most wear, exhibiting micro-cracking, chipping and flaking at the exit orifice edge.

Performance of 3C-SiC thin films as protective coatings for silicon-micromachined atomizers

This paper presents a study of the deposition and performance of 3C-silicon carbide (3C-SiC) coatings on the flow surfaces of silicon micromachined fuel atomizers. Atmospheric pressure chemical vapor deposition (APCVD) was used to grow 3C-SiC on atomizer features which were fabricated from silicon wafers using deep reactive ion etching (DRIE). The 3C-SiC films were shown to be conformal across high-aspect-ratio atomizer structures which were etched to depths greater than 250 μm. For tests conducted at pressures up to 690 kPa, the SiC-coated atomizers had wider spray angles, equivalent Sauter Mean Diameters (SMD), and an 11% increase in flow rates when compared to uncoated atomizers. Erosion tests proved that the SiC coating can dramatically increase the service life of silicon fuel atomizers.

Progress on Comparison Study of the Erosion of Conventionally Machined and Macrolaminated Pressure-Swirl Atomizers

Gas turbine fuel atomization nozzles are subject to internal erosion damage caused by the flow of the liquid fuel and its inevitable contaminants. Nozzles must be sufficiently erosion resistant, or erosion tolerant, to insure acceptable performance throughout their design life. Recently developed macrolamination (ML) technology for construction of pressure-swirl nozzles shows potential performance, cost, and size benefits when compared to conventionally constructed nozzles. The objective of this study is to compare macrolaminated and conventional nozzles under identical accelerated erosive conditions to determine their relative wear characteristics. To date, twelve nozzles have been compared with some being disregarded because of anomalies. It is shown that erosion damage results in increased flow rates. Also, the tendencies shown are for conventional nozzles to erode to narrower spray angles and macrolaminated nozzles to erode to wider spray angles. ML nozzles exhibit some important failure modes that differ from nozzles of conventional design.Copyright