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Research and Development The APS Materials technical staff uses a wide range of advanced plasma spray equipment to provide for every coating need. We are unique in our ability to conduct coating research in vacuum and inert gas chambers. More consistent coating properties is gained by the use of Robotic manipulation of the spray equipment, and materials that easily oxidize or decompose in normal air plasma spraying can be accommodated in one of our spray chambers. Various thermal spraying systems available for R&D activities include: ·
R&D projects we have conducted have covered a multitude of applications and materials. A partial listing of recent R&D activities is shown below. ·
Some of the materials investigated in recent R&D projects include the following: ·
APS Materials Testing Laboratory During the early 1980’s, The APS Materials’ Testing Laboratory (APSMTL) was born out of the needs of our aerospace coatings division. Since that time, our customer’s coating requirements have made the use of the test lab a necessity by every industry we serve. Our specially trained technical staff allows us to insure quality and consistency in our coating systems and manufactured products. Accordingly, the testing equipment is routinely calibrated and maintained to ensure the reliability and quality of our test results per NADCAP and ISO standards. Specific tests performed by our test lab include: Tensile testing provides us with a quantitative measurement of the bond strength of a particular coating to a particular substrate. The type of coating failure during the test can provide important information about the coating-substrate system. Critical applications, such as plasma sprayed coatings on jet engine components, usually require the periodic tensile testing of test specimens to ensure that the process is controlled. Our experienced technical staff can provide a detailed analysis of any coating failure. A Tinius Olsen tensile test machine is used to determine the maximum load force to rupture the coating and/or substrate. Test specimens are made in the form of 1” diameter cylinders, coated on one side. Tensile strength is calculated using the equation: Tensile strength, psi = maximum load force/surface area The test specimen is attached to the tensile test fixture using a high strength adhesive, and the tensile load is applied perpendicular to the coating surface until the point of rupture. Aerospace companies have adopted lap shear strength to determine the maximum shear force required to fracture a coating. This process is similar to conventional tensile tests. First, mating lap shear panels are coated on one side and adhesively bonded to each other. A conventional tensile test machine with the appropriate fixtures is used to apply a known load force. The lap shear strength is then calculated from the equation: Lap shear strength, psi= maximum load force/coating area This is a standard method of measuring the shear strength of coatings for biomedical and other applications. The test specimens are similar to those used for tensile strength tests. However, the tensile machine test fixture is designed apply a shear force parallel to the coating surface. At failure, the maximum shear strength of the coating is determined. Macrohardness is determined using a Rockwell hardness tester and a diamond indentor. The hardness value is an important indicator of the coating density, wear resistance, and overall integrity. The hardness value is determined by considering the kilogram load and the depth of penetration. Our trained staff must take care to measure only the coating hardness and not the combined substrate-coating hardness. The hardness of thin coatings on a test specimen can be accurately determined per the appropriate aerospace or ASTM specification by establishing a minimum coating thickness and the appropriate indentor/load combination. This test is particularly useful in determining the physical characteristics of brittle materials, such as ceramic coatings and structures. Similar to macrohardness, it is an important indicator of the coating density, wear resistance, and particle-to-particle cohesion. Microhardness is determined by using a Vickers hardness tester. A diamond indentor creates an indentation in the test specimen, and the microhardness value is then determined as a function of the dimensions of the indentation and the gram load force. Metallography takes a closer look at the actual structure of the material in order to evaluate coatings or solid shapes. Coating microstructure can be an important method of determining and maintaining coating quality. The test specimen is prepared by orienting and mounting the specimen in a supporting medium and then polishing to expose the microstructure. The sample can then be examined using an optical metallograph. In many cases, the evaluation is aided by the use of photo standards of similar microstructures with various types of defects. Coatings are routinely examined for evidence of unmelted particles, metallic inclusion, voids/porosity, spalling, micro-cracking, and embedded contaminants. Metallic coatings can also be examined for oxide content. In addition, image analysis methods can be used to quantitatively determine the amount of a particular component material and or percent of porosity. The application of coatings to titanium alloy and other substrates can, if done improperly, result in lowered fatigue strength. The APSMTL performs fatigue testing to measure any changes in fatigue properties after processing by employing a test machine to apply reverse bending loads to straight shanked specimen bars. Typically, the coating is applied to the center portion of the test bar, and the bars are subjected to a large number of reverse bending load cycles until either a failure or a successful run out of 10 million cycles occurs. Test procedures for biomedical coatings are given in ASTM F1160-98. Abrasion testing provides information concerning the wear resistance, toughness, and overall stability of a material subjected to a light load rubbing or shearing action. It also has been found to provide valuable information about the formation of debris in biomedical coatings. The FDA and others have adopted test methods to evaluate a variety of coatings. The APSMTL can perform this test to determine the quality of a particular coating or material for a customer’s application. As an example, abrasion resistance of plasma sprayed porous coatings of CPTi and Ti alloys are performed on 4”X4” coated panels. The panels are rotated while in contact with a wear surface of known hardness and composition. The panels are weighed after a specific number of rotation cycles and the data compared to known standard materials or previously processed coatings. Our in-house testing capabilities give APS Materials, Inc. the ability to closely regulate the quality of the coatings we produce and provide for our customers. By monitoring the coating process, we are able to precisely engineer coatings to fill our customer’s specific needs. All laboratory-testing results are recorded and subjected to statistical analysis, and statistical process control is routinely used to ensure quality in our coated products.
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© 2008 - APS Materials, Inc.
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