Metal coatings have been widely utilized in metal production for protective functions or to increase mechanical/chemical qualities of product surfaces. These metal coatings improve protection against corrosion, aid in abrasion/temperature resistance, and enhance the electrical conductivity of the metal. Additionally, metal coatings boost cohesion, solderability, and lubricity in materials. Under-coating might result in product degradation and failure. Optimizing the coating thickness layer helps prevent these setbacks and guarantees the products have the appropriate qualities while also optimizing manufacturing costs. Optimizing the coating thickness layer is crucial in the industries such as: metallic finishing, automotive, aerospace, and more.
Substances are coated, plated, and polished to optimize functional behavior and prolong life expectancy. The coating density and thickness must be within the stated specified allowance. If somehow the layer is too thin, then oxidation, corrosion, or an improper electrical connection may occur and cause the finished component to malfunction prematurely in the environment. Coatings that are too thick might interfere with the fit of intricate and complex geometry like engine components. When it comes to aesthetic coatings, obtaining the perfect thickness is crucial for giving the end product a flawless look. If this isn’t done correctly, the product may have to be redone or thrown away.
The problem is determining how to monitor coating thickness on completed components precisely and consistently. There might be multiple layers to examine and the measurement method should not harm or fundamentally alter the product’s appearance whatsoever. That is where the X-ray fluorescence analyzers and electromagnetic connection gauges come into play. These quantitative techniques are fast, precise, and highly non-destructive, enabling you to obtain essential observations on coated items or completed installations in moments.
Coating Thickness Evaluation with Non-Destructive Testing (NDT) Mechanics and Technologies
For quality management, various non-destructive screening procedures are developed to evaluate the thickness dimensions of metallic coatings in real-time. These solutions are commonly utilized in metal finishing firms or throughout the raw product assessment process in sectors that use coated materials. The particular magnetic pull-off and electromagnetic induction gauges monitor non-magnetic finishes in metallic materials. Micro-resistance processes are ideal for measuring the thickness dimensions of metal films or on nonmetallic surfaces. A radioactive isotope-based methodology, beta beam backscatter, can measure the thickness dimensions of metal coatings over a surface if the material and plating layer have significantly different atomic numbers or densities.
X-ray fluorescence (XRF) spectroscopy is yet another technique for determining the thickness measurements of metal coatings. The XRF methodology involves irradiating a sample with just a small X-ray tube and measuring the produced radiation signature from elements present in the protective films and materials. XRF can determine the thickness of individual and numerous coatings of metal coverings over every other kind of material depending on the characteristics of the detected frequencies for each constituent. This makes it highly adaptable to other methods. Elements like Magnesium (Mg) can be measured using XRF. Based upon the density values, the relative atomic number of such protective film, and the frequency of the emission lines utilized, XRF may measure the weight as well as thickness of substantially thin covering films of very few atomic thicknesses up to the saturation thickness.
Coating thickness was previously measured with XRF utilizing stationary and benchtop equipment. However, monitoring coating thickness on large items without cutting specimens is impractical since the material must be carried within or adjacent to the spectrum analyzer compartment for examination utilizing static XRF methodologies. Online XRF equipment, an excellent technique for metal plus alloy detection, can circumvent this constraint.
Calibration Methods
The calibration methodology used in conventional and online X-ray fluorescence is of the utmost importance. The metal floor and the metal covering film produce distinct frequencies in X-ray fluorescence technology. The absorption rate of information from the material or the radiation of particular coating films could both be used to measure penetration depth. A correlation between analytical transmissions and the Coating Weight gauges for quantitative calibration measures (or previously defined reference specimens) must be established. Designing subjective calibration models and frameworks is one option. For single coverings, arithmetic is easy, but non-linear models are required with several layers. Many requirements are necessary for multi-layer covering systems, which might not be readily accessible or convenient to fabricate.
Modern devices are using a theoretical approach for standardless primary parametric calibration. Under this scenario, an algorithm employs physical constants to simulate the sample’s mechanical attributes from spectral observations iteratively. This algorithm seems to be capable of handling multi-layer coverings and materials of various compositions. The term “standardless” refers to the capability of the operator to conduct observations without the utilization of quantitative calibration criteria as seen on general industry specification requirements. Yet, it is advisable to utilize comparable standards to test the precision of the equipment and implement changes to increase efficiency as appropriate.
Ideas and examples
Even though the primary parameter technique is flexible, it is necessary to understand and characterize the material makeup, layer sequencing, and layer concentration before starting the evaluation. Data may be recorded via the device’s user interface. The material during this first sample is composed of mild alloy steel. Its first coating is Zinc. Its second coating is a thin film of Zirconium. Such a form of zirconium-coated galvanized steel is used in many industries. The zinc coating keeps the steel from oxidizing, whereas the zirconium coating boosts corrosion resistance and provides improved paint adhesion.
Another example of coating aiding in the general industry is with material like Kovar, a nickel-cobalt ferrous alloy. Kovar has a thermal expansion coefficient identical to material like glass utilized for glass encapsulation in instruments like microwaves or X-ray tunnels. Electroless nickel coating, a nickel-phosphorus alloy that offers significant corrosion and wear resistance, is applied to the Kovar material. This method is difficult to perform for a few reasons: the material and the covering are alloy materials. Both include large amounts of nickel. The enhanced fundamental parameter’s automated system can accurately ascertain the thickness value of electroless nickel out over Kovar alloy using all these emissions as well as absorption.
Typical coating thickness assessment applications
- Electromagnetic instruments
- Example:
- Through-hole and surface-mounted PCB copper density and depth.
- X-ray fluorescence for plating density and makeup of final coatings.
- Example:
- Electroplating where X-ray fluorescence is used to determine plating thickness values, concentration, & electromagnetic thickness measurement gauges enabling testing electroplated coatings on a variety of materials.
- Micro-connections, lead frameworks, interconnects, and cable connectors
- X-ray fluorescence plus electromagnetic gauges, particularly for Zinc covering thickness analysis, are used with hot-dip or electro-galvanizing processes.
- Handheld electromagnetic virtual thickness gauges for automotive, aerospace, and powder protective coating.
- Electromagnetic instruments for determining the thickness of anodized layers
Summary
Metal finishing companies and other industries that use metals can use handheld X-ray Fluorescence Spectroscopy to check that metallic coat weight plus coating thickness standards are satisfied. International procedures, including the ISO 3497 and ASTM B568, can be used by operators to conduct an evaluation. Handheld X-ray Fluorescence Spectroscopy is a valuable instrument for quality inspection and monitoring that offers numerous advantages, such as:
- The evaluation of alloy quality and makeup of materials.
- Product failures are minimized and manufacturing costs are optimized.
- Effectively scan for thin areas that would compromise corrosion resistance.
- Process control for coatings that are too thick. Reduces waste in coating.
- A non-destructive inspection technique is utilized. No need to destroy high-value products.
- Multiple inspections ensure constant coating across any component, which improves quality.
- No need for specimen preparation.
- Quality assurance evaluations and certificates are generated.