Location

Seattle, WA

Start Date

1-1-1996 12:00 AM

Description

Thermal spraying of protective coatings has been in use since 1917 when the initial application was the spraying of zinc layers onto steel structures to prevent corrosion [1]. In the 1970’s plasma-spray technology was first used with the introduction of vacuum plasma-spraying [1]. Today, gases such as argon and nitrogen (sometimes with an additional gas such as helium or hydrogen) are often used in plasma-spray guns. In plasma-spraying an electric-arc discharge heats the gas stream to high temperature (≥ 10,000 K), turning it into a plasma. The gas exits the spray-gun at high speed (≈ 200 m/s to 600 m/s) towards the material to be coated. Material powder (often carried by a second gas stream) is injected into the plasma stream, where it melts into liquid droplets. These droplets are carried onto the target surface, where they rapidly cool (≈ 106 K/s) into solid, flat splats. A layer of material can be built up by repeated spraying of the same surface area. This high-temperature process allows for the spraying of virtually any material possessing a stable molten phase, including ceramics [2]. Further technical details and the history of plasma-spraying can be found in [1–2].

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

15B

Chapter

Chapter 6: Material Properties

Section

Coatings

Pages

1613-1620

DOI

10.1007/978-1-4613-0383-1_211

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Ultrasonic NDE of Sprayed Ceramic Coatings

Seattle, WA

Thermal spraying of protective coatings has been in use since 1917 when the initial application was the spraying of zinc layers onto steel structures to prevent corrosion [1]. In the 1970’s plasma-spray technology was first used with the introduction of vacuum plasma-spraying [1]. Today, gases such as argon and nitrogen (sometimes with an additional gas such as helium or hydrogen) are often used in plasma-spray guns. In plasma-spraying an electric-arc discharge heats the gas stream to high temperature (≥ 10,000 K), turning it into a plasma. The gas exits the spray-gun at high speed (≈ 200 m/s to 600 m/s) towards the material to be coated. Material powder (often carried by a second gas stream) is injected into the plasma stream, where it melts into liquid droplets. These droplets are carried onto the target surface, where they rapidly cool (≈ 106 K/s) into solid, flat splats. A layer of material can be built up by repeated spraying of the same surface area. This high-temperature process allows for the spraying of virtually any material possessing a stable molten phase, including ceramics [2]. Further technical details and the history of plasma-spraying can be found in [1–2].