Papers by Author: Mattison K. Ferber

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Authors: Hua Tay Lin, Mattison K. Ferber
Abstract: This paper summarizes the recent results on component characterization efforts carried out to verify the mechanical reliability of SN237 and SN281 silicon nitride microturbine rotors manufactured by Kyocera. Mechanical properties of biaxial discs machined from airfoils of microturbine rotors were evaluated by a ball-on-ring test technique. Results showed that the mechanical properties of samples from airfoils with as–processed surfaces exhibited lower characteristic strength than those machined from the hub region with as-machined surfaces. The differences in mechanical performance and reliability between asprocessed components and simple-shaped test coupons appear to arise mainly from differences in strength limiting flaw type and population.
Authors: M.N. Menon, H.T. Fang, D.C. Wu, M.G. Jenkins, Mattison K. Ferber
Authors: Mattison K. Ferber, Hua Tay Lin
Abstract: Over the last 30 years, a number of programs in Russia, Europe, Japan, and the United States have sought to introduce monolithic ceramic components into gas turbines with the goals of increasing efficiency and lowering emissions. High performance silicon nitride and silicon carbide ceramics typically have been leading candidates for use in these applications. Recent field tests involving silicon nitride vanes and blades have shown that these materials can experience significant recession due to the loss of the normally protective silica scale. This paper first summarizes key findings from these field tests and then describes a relatively simple method for evaluating environmental effects in a laboratory environment.
Authors: Edgar Lara-Curzio, Mattison K. Ferber, P.F. Tortorelli
Authors: Paul F. Becher, Gayle S. Painter, Naoya Shibata, Hua Tay Lin, Mattison K. Ferber
Abstract: Silicon nitride ceramics are finding uses in numerous engineering applications because of their tendency to form whisker-like microstructures that can overcome the inherent brittle nature of ceramics. Studies now establish the underlying microscopic and atomic-scale principles for engineering a tough, strong ceramic. The theoretical predictions are confirmed by macroscopic observations and atomic level characterization of preferential segregation at the interfaces between the grains and the continuous nanometer thick amorphous intergranular film (IGF). Two interrelated factors must be controlled for this to occur including the generation of the elongated reinforcing grains during sintering and debonding of the interfaces between the reinforcing grains and the matrix. The reinforcing grains can be controlled by (1) seeding with beta particles and (2) the chemistry of the additives, which also can influence the interfacial debonding conditions. In addition to modifying the morphology of the reinforcing grains, it now appears that the combination of preferential segregation and strong bonding of the additives (e.g., the rare earths, RE) to the prism planes can also result in sufficiently weakens the bond of the interface with the IGF to promote debonding. Thus atomic-scale engineering may allow us to gain further enhancements in fracture properties. This new knowledge will enable true atomic-level engineering to be joined with microscale tailoring to develop the advanced ceramics that will be required for more efficient engines, new electronic device architectures and composites.
Authors: S.M. Zemskova, Hua Tay Lin, Mattison K. Ferber, A.J. Haynes
Abstract: Previous studies have demonstrated that dense coatings of CVD mullite (3Al2O3×2SiO2) provide excellent oxidation protection for Si3N4 and SiC in a high pressure, steam environment. In this study the mechanical properties of CVD mullite coated silicon nitride materials from different vendors (AS800, NGKSN88, Kyocera SN281) were evaluated following ASTM test procedures. The dynamic fatigue tests werep erformed in ambient air at temperatures of 850 and 1200°C under fast (30 MPa/s) and slow (0.003 MPa/s) load rates. The static fatigue tests were carried out at a constant load of 350 MPa for 1000h at 1200°C. The cyclic fatiguetests at 850°C consisted of a loading ramp from 20 to 400 MPa in 30 seconds followed by unloading ramp from 400 to 20 MPa. A total of 10,000 cycles were applied to the fatigue test specimens before fast fracture tests were conducted at room temperature. The strength test results indicated that CVD mullite coatings showed excellent adhesion during dynamic fatigue tests and exhibited no creep behavior. Minor flexure strength reduction observed at low stressing rate and at high temperatures appeared to be related to Si3N4 properties such as SCG (slow crack growth) susceptibility. During cyclic and static fatigue tests, a glassy silica/aluminosilicate phase was formed due to oxidation. This resulted in localized coating separation and buckling. However, accumulation of this corrosion layer was not critical since the coated specimens showed a flexure strength increase of ~7-9.5%.
Authors: Hao Tung Lin, Paul F. Becher, Mattison K. Ferber, V. Parthasarathy
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