Jeffrey A. Brogan

The 2016 Thermal Spray Roadmap

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.

The coalescence of combustion-sprayed ethylene–methacrylic acid copolymer

A design of experiments approach was employed to study the coalescence of combustion-sprayed ethylene-methacrylic acid copolymer (EMAA). The powder feed rate, stand-off distance, substrate temperature, propane flow rate, and compressed air flow rate were studied by using a 25-1 factorial design matrix. Empirical models were developed to predict coating surface roughness, coating temperature and splat elongation ratio. Such methods allow process optimization, estimation of interactions among parameters, and the determination of the factors which influence the coalescence of ethylene-methacrylic acid copolymer coatings.

Embedded temperature and heat flux sensors for advanced health monitoring of turbine engine components

MesoScribe Technologies has developed a process for producing embedded, conformal, thick film sensors based on direct write technology. Thermocouple and heat flux sensors can be fabricated directly onto engineering components and embedded into functional coatings. This provides for a variety of vital advantages: reliability, robustness and survivability in extremely harsh environments, cost effective implementation, and fabrication onto surfaces that are large, conformal (non-flat) and flexible. Embedded thermocouples and heat flux sensors were deposited onto superalloy substrates and subjected to a number of high temperature tests including isothermal furnace heating, cyclic burner rig testing, and continuous flame impingement. Initial testing yields Seebeck coefficients within 3% of commercial thermocouples. Results also demonstrate that embedded Type K thermocouples survive over 200 thirty minute burner rig cycles with surface temperatures exceeding 1150degC. Embedding thermocouples at different depths within the TBC allows for simultaneous temperature measurements within the temperature gradient. In addition, over 20 hours of continuous flame impingement have been recorded with stable output. Embedded thermocouples were also tested at NASA GRC using a 3.5 kW CO 2 high heat flux laser which also allows extraction of thermal conductivity. The test comprised of 75 thirty minute cycles with a surface temperature of 1150degC and metal interface temperature of 930degC for a total duration of 41 hours. This very first test showed the capability of the embedded TC in terms of performance and durability. This paper summarizes the harsh environment test results as well as provides an overview of the capabilities of direct write technology to instrument propulsion and space structures

Embedded resistive strain sensors for harsh environments

Strain gages developed using high-definition direct write technology enable direct bonding to substrates without an adhesive layer, so greater shear forces may be faithfully transmitted and thicker, more robust conductors may be used for strain-sensing. Effects of hysteresis, creep, and temperature limitations common to adhesively-bonded gages can also be mitigated. Manufacture and installation of the gage (and lead wires) are automatic and simultaneous, reducing preparation time and cost. Using the above developed method, industrial-grade strain gages have been fabricated and tested. Standard gage resistances between 120Omega-350Omega have been achieved on grids smaller than 10mm2 using nickel-chrome as the gage material. Thermal plasma-sprayed laser-cut resistive gages have achieved gage factors of 1.3, operating linearly and repeatably for more than 105 cycles between plusmn1000muepsiv. Additional performance metrics, e.g. temperature sensitivity and compensation, were treated in this paper

Mechanical properties of metal- and ceramic-polymer composites formed via thermal spray consolidation—Extended abstract

Polymeric composites, with either metallic or ceramic fillers, have been manufactured by thermal spray, and their mechanical properties have been measured. The advantage of this technology is that it allows on-site manufacture and is a repairable composite system, with virtually no cure time and no release of volatile organic compounds. Fracture mechanisms have been studied to examine mechanical modeling of the composite system.

High temperature telemetry systems for in situ monitoring of gas turbine engine components

Monitoring the health of engine components in-situ and in real-time is critical for reducing life cycle costs of military aircraft, such as F-35. As aircraft complexity and performance requirements increase, inspection-based maintenance at pre-defined intervals becomes costly and insufficient. A more efficient approach is to integrate sensor systems, capable of withstanding harsh operating environments, to provide real-time diagnostics and support condition-based maintenance and failure prognostics.

Development and F-Class Industrial Gas Turbine Engine Testing of Smart Components With Direct-Write Embedded Sensors and High Temperature Wireless Telemetry

The potential for savings provided to worldwide operators of industrial gas turbines, by transitioning from the current standard of interval-based maintenance to condition-based maintenance may be in the tens of millions of dollars per year. Knowledge of the historical and current condition of life-limiting components will enable more efficient use of industrial gas turbine resources via increased operational flexibility, with less risk of unplanned outages as a result of off-parameter operations. To date, it has been impossible to apply true condition-based maintenance to industrial gas turbines because the extremely harsh operating conditions in the heart of a gas turbine preclude using the necessary advanced sensor systems to monitor the machine’s condition continuously. The U.S. Department of Commerce’s National Institute of Standards and Technology – Advanced Technology Program (NIST-ATP) awarded the Joint Venture team of Siemens Power Generation, Inc. and MesoScribe Technologies, Inc. a four-year,

Physical and Relaxation Properties of Flame-Sprayed Ethylene -Methacrylic Acid Copolymer

5.4 million program in November, 2004, titled Conformal, Direct-Write-Technology-Enabled, Wireless, Smart Turbine Components. The target was to develop a potentially industry-changing technology to build smart, self-aware engine components that incorporate embedded, harsh-environment-capable sensors and high temperature capable wireless telemetry systems for continuously monitoring component condition in both the compressor and turbine sections. The approach involves several difficult engineering challenges, including the need to embed sensors on complex shapes, such as turbine blades, embedding wireless telemetry systems in regions with temperatures that preclude the use of conventional silicon-based electronics, protecting both sensors and wireless devices from the extreme temperatures and environments of an operating gas turbine, and successfully transmitting the sensor information from an environment very hostile to wireless signals. The program included full-scale, F-class industrial gas turbine engine test demonstrations with smart components in both the compressor and turbine sections. The results of the development program and engine testing to date will be discussed.Copyright