High Frequency Longitudinal and Shear Wave Inspection of Gas Turbine Ceramics

To assure reliable performance of ceramic materials in gas turbine engines, where performance at 1400°C for up to 10,000 hours is required, it is necessary to screen out material with defects in the size range 10 to 100 μm (0.0004 to 0.004 inches). Investigation of high frequency ultrasonic techniques has led to development of longitudinal and shear wave methods capable of detecting defects at least down to 25 μm In size. The approach is to use a high frequency (45 MHz) ultrasonic pulse-echo Immersion mode technique, making C-scan recordings of the results. Inspections have been performed on hot pressed and reaction bonded silicon nitride and hot pressed and sintered silicon carbide. Natural defects, seeded Inclusions, and artificial surface cracks have been examined. Reference standards of hot pressed silicon nitride containing seeded defects and laser drilled holes have been developed. Four-point-bend testing and scanning electron microscopy have been employed to establish correlation with ultrasonic results

Ultrasonic Detection of Surface Flaws in Gas Turbine Ceramics

This paper presents the results of a program sponsored by NADC for NASC to develop an ultrasonic surface wave technique for detection of small flaws, \u3c100 11m (\u3c 0.004 inch), in gas turbine quality ceramics. A 45 MHz ultrasonic surface wave inspection technique is described, which employs immersion scanning ndd C-scan recording. Inspection results are presented using this technique on specimens of hot pressed Silicon nitride and silicon carbide, from two sources each, and reaction bonded silicon nitride. Results are also presented of four-point-bend tests and scanning electron micrography, which were used to identify defect sizes and types and to correlate flexural strength with inspection results. The flexural strength is shown to correlate, at least qualitatively, with the extent of ultrasonic response from machining damage. The sensitivity to individual defects is shown to be limited primarily by the extent of machining damage and the spot size of the ultrasonic beam

Airfoil

Although the method and apparatus of the present invention can be utilized to apply either a uniform or a nonuniform covering of material over many different workpieces, the apparatus (20) is advantageously utilized to apply a thermal barrier covering (64) to an airfoil (22) which is used in a turbine engine. The airfoil is held by a gripper assembly (86) while a spray gun (24) is effective to apply the covering over the airfoil. When a portion of the covering has been applied, a sensor (28) is utilized to detect the thickness of the covering. A control apparatus (32) compares the thickness of the covering of material which has been applied with the desired thickness and is subsequently effective to regulate the operation of the spray gun to adaptively apply a covering of a desired thickness with an accuracy of at least plus or minus 0.0015 of an inch (1.5 mils) despite unanticipated process variations

Method and apparatus for use in making an object

Although the method and apparatus of the present invention can be utilized to apply either a uniform or a nonuniform covering of material over many different workpieces, the apparatus (20) is advantageously utilized to apply a thermal barrier covering (64) to an airfoil (22) which is used in a turbine engine. The airfoil is held by a gripper assembly (86) while a spray gun (24) is effective to apply the covering over the airfoil. When a portion of the covering has been applied, a sensor (28) is utilized to detect the thickness of the covering. A control apparatus (32) compares the thickness of the covering of material which has been applied with the desired thickness and is subsequently effective to regulate the operation of the spray gun to adaptively apply a covering of a desired thickness with an accuracy of at least plus or minus 0.0015 inches (1.5 mils) despite unanticipated process variations

Control apparatus

Although the method and apparatus of the present invention can be utilized to apply either a uniform or a nonuniform covering of material over many different workpieces, the apparatus (20) is advantageously utilized to apply a thermal barrier covering (64) to an airfoil (22) which is used in a turbine engine. The airfoil is held by a gripper assembly (86) while a spray gun (24) is effective to apply the covering over the airfoil. When a portion of the covering has been applied, a sensor (28) is utilized to detect the thickness of the covering. A control apparatus (32) compares the thickness of the covering of material which has been applied with the desired thickness and is subsequently effective to regulate the operation of the spray gun to adaptively apply a covering of a desired thickness with an accuracy of at least plus or minus 0.0015 inches (1.5 mils) despite unanticipated process variations

High Frequency Longitudinal and Shear Wave Inspection of Gas Turbine Ceramics

To assure reliable performance of ceramic materials in gas turbine engines, where performance at 1400°C for up to 10,000 hours is required, it is necessary to screen out material with defects in the size range 10 to 100 μm (0.0004 to 0.004 inches). Investigation of high frequency ultrasonic techniques has led to development of longitudinal and shear wave methods capable of detecting defects at least down to 25 μm In size. The approach is to use a high frequency (45 MHz) ultrasonic pulse-echo Immersion mode technique, making C-scan recordings of the results. Inspections have been performed on hot pressed and reaction bonded silicon nitride and hot pressed and sintered silicon carbide. Natural defects, seeded Inclusions, and artificial surface cracks have been examined. Reference standards of hot pressed silicon nitride containing seeded defects and laser drilled holes have been developed. Four-point-bend testing and scanning electron microscopy have been employed to establish correlation with ultrasonic results.</p

High Frequency Longitudinal and Shear Wave Inspection of Gas Turbine Ceramics

To assure reliable performance of ceramic materials in gas turbine engines, where performance at 1400°C for up to 10,000 hours is required, it is necessary to screen out material with defects in the size range 10 to 100 μm (0.0004 to 0.004 inches). Investigation of high frequency ultrasonic techniques has led to development of longitudinal and shear wave methods capable of detecting defects at least down to 25 μm In size. The approach is to use a high frequency (45 MHz) ultrasonic pulse-echo Immersion mode technique, making C-scan recordings of the results. Inspections have been performed on hot pressed and reaction bonded silicon nitride and hot pressed and sintered silicon carbide. Natural defects, seeded Inclusions, and artificial surface cracks have been examined. Reference standards of hot pressed silicon nitride containing seeded defects and laser drilled holes have been developed. Four-point-bend testing and scanning electron microscopy have been employed to establish correlation with ultrasonic results.</p

Ultrasonic Detection of Surface Flaws in Gas Turbine Ceramics

This paper presents the results of a program sponsored by NADC for NASC to develop an ultrasonic surface wave technique for detection of small flaws, <100 11m (< 0.004 inch), in gas turbine quality ceramics. A 45 MHz ultrasonic surface wave inspection technique is described, which employs immersion scanning ndd C-scan recording. Inspection results are presented using this technique on specimens of hot pressed Silicon nitride and silicon carbide, from two sources each, and reaction bonded silicon nitride. Results are also presented of four-point-bend tests and scanning electron micrography, which were used to identify defect sizes and types and to correlate flexural strength with inspection results. The flexural strength is shown to correlate, at least qualitatively, with the extent of ultrasonic response from machining damage. The sensitivity to individual defects is shown to be limited primarily by the extent of machining damage and the spot size of the ultrasonic beam.</p

Ultrasonic Detection of Surface Flaws in Gas Turbine Ceramics

This paper presents the results of a program sponsored by NADC for NASC to develop an ultrasonic surface wave technique for detection of small flaws, <100 11m (< 0.004 inch), in gas turbine quality ceramics. A 45 MHz ultrasonic surface wave inspection technique is described, which employs immersion scanning ndd C-scan recording. Inspection results are presented using this technique on specimens of hot pressed Silicon nitride and silicon carbide, from two sources each, and reaction bonded silicon nitride. Results are also presented of four-point-bend tests and scanning electron micrography, which were used to identify defect sizes and types and to correlate flexural strength with inspection results. The flexural strength is shown to correlate, at least qualitatively, with the extent of ultrasonic response from machining damage. The sensitivity to individual defects is shown to be limited primarily by the extent of machining damage and the spot size of the ultrasonic beam.</p