Compressor abradables coming into operational contact with bare, un-tipped titanium alloy rotor blades over a wide range of incursion conditions require excellent cuttability in order to avoid blade tip damage by wear and over-heating. This is more easily achieved for low temperature systems that can make use of low shear strength aluminum matrices than for compressor abradables operating closer to the maximum allowable temperature of advanced titanium alloy blade materials. In this case the rotor path linings will have to incorporate higher temperature resistant Ni and Co alloy matrices. To that end the availability of abradable coatings capable of operating at up to 550°C while showing little thermal ageing effects and excellent abradability over their entire service life can influence the compressor blade material selection and therefore compressor weight and performance characteristics. This paper provides an overview of titanium blade friendly compressor abradable concepts. Particular emphasis will be placed on the abradability of in-service and next-generation coatings designed for use up to the temperature capability of Ti blade rotor materials and beyond. Candidate coatings are also screened for other performance criteria such as thermal cyclic resistance and ageing behaviour.

Traditional fused and crushed (F&C) titania feedstock powders have relatively poor flow and are limited in the feed-rates that can be achieved before deposition efficiencies (DEs) start to decline. In addition, the coatings made with F&C powders generally have high stiffness and limited fracture toughness. Such coatings bear the risk of cracking/delaminating particularly in the case of thick coatings. To address these issues, a new agglomerated and sintered (A&S) titania feedstock powder has been developed and compared in side-by-side spray tests to the traditional F&C titania powder of comparable particle size. The spray behavior, achievable feed-rates and DEs, as well as the resulting coating characteristics were evaluated from the view point of their application as thick, electrically conductive coatings. The new A&S powder yields up to approximately 200% improvement in DE while producing coatings with more suitable microstructure, lower electrical resistivity and higher thickness. Furthermore, for a given set of process parameters, the DEs obtained with this new powder show little sensitivity to the powder feed-rates, thus allowing spraying at higher feed-rates without compromising coating DEs. This feature of the powder has significant commercial advantages for thick coatings when combined with high throughput guns such as TriplexPro-200. Preliminary results of particle diagnostics towards understanding of the fundamental principles behind these improvements are also discussed.

Abradable seals have been used in jet engines since the late 1960's. Today they are seeing applications in low pressure and high pressure sections of compressors as well as the high pressure turbine module of jet engines. Clearance control systems using abradable coatings are also gaining ever more attention in industrial and steam turbine applications. Thermal spraying is a relatively simple and cost effective means to apply abradable seals. Abradable coatings work by minimizing gaps between rotating and stationary components by allowing the rotating parts to cut into the stationary ones. Typically plasma and combustion spray processes are used for applying abradable coatings. The types of coatings employed in the HP turbine are zirconia based abradable material systems with polymer and, in some cases, solid lubricant additions such as hexagonal boron nitride. The coatings are designed to work at service temperatures of up to 1200°C. Types of matrix materials used in the low and high pressure sections of the compressor are aluminum-silicon, nickel and MCrAlY based systems. These compressor type systems typically also contain fugitive phases of polymer and/or solid lubricants such as hexagonal boron nitride or graphite. Operating temperature, depending on the material of choice, can be up to 750°C. Regardless of the specific application, fugitive phases and porosity are needed for abradable coatings. Polymers are used to create and control porosity in plasma sprayed coatings, a critical design requirement in adjusting abradability and erosion properties of thermal spray coatings. Combustion spray coatings generate porosity through the lower deposition velocities and temperatures compared to plasma and typically do not need polymer phases. Solid lubricants are added to help weaken the structure of thermal spray coatings and reduce frictional heating and material transfer to the blade.

Advanced RF IC’s incorporate numerous components along with the CMOS circuitry. One component is a metal-insulator-metal (MIM) capacitor. Test capacitors have been stressed using accelerated voltage and temperature conditions to assess the long-term reliability. This paper describes a methodology for evaluating the MIM capacitors that have failed during reliability testing. IR microthermography was developed to detect leakage locations in areas that are not visible to optical inspection or standard emission microscopes. These areas were deprocessed to correlate the IR emission and physical defect locations. This information is utilized to understand the failures and improve the reliability.

In order to understand spatial and temperature resolution limits of an infrared microscope used for fault location in semiconductor devices, numerical models and bench methods are correlated and discussed. Results clearly show fault identification capability in the sub-micron realm and “hot-spot” resolution of a few tenths of a degree K.

Visible to infra-red photon emissions can be readily observed in compound semiconductor devices through the semi-insullating substrate and are useful in fault identification when analyzing yield problems. The techniques described here have uncovered several yield-limiting mechanisms and have lead to rapid and effective corrective measures.