The stress distribution between the coating and the substrate of spring steel plated with colorful coatings is a core factor affecting its service performance. Its detection and analysis must be conducted comprehensively, considering material properties, stress types, and actual operating conditions. The stress between the coating and the substrate mainly originates from differences in thermal expansion coefficients, mismatches in elastic moduli, and process effects during coating deposition. For example, colored coatings are typically prepared using physical vapor deposition (PVD) or chemical vapor deposition (CVD). During deposition, rapid atomic accumulation easily forms internal stress. Furthermore, the difference in thermal expansion coefficients between the coating and the substrate induces thermal stress with temperature changes. If these stresses are not effectively controlled, they may lead to coating cracking, peeling, or decreased substrate fatigue performance, thus affecting the durability and reliability of the spring steel.
The first step in detecting the stress distribution between the coating and the substrate is to identify the stress type and distribution characteristics. Stress can be divided into macroscopic residual stress and microscopic localized stress. The former is generated by the interaction between the overall coating and the substrate, while the latter originates from the coating's grain structure, defects, or interfacial bonding state. The stress distribution of spring steel plated with colorful coatings is typically non-uniform, especially at coating edges, pores, or areas of abrupt changes in substrate surface roughness, where stress concentrations easily form. These areas are potential starting points for crack initiation. Therefore, testing must cover the overall stress state of the coating and localized high-stress areas to comprehensively assess the impact of stress on performance.
X-ray diffraction is a classic method for detecting residual stress in coatings. Its principle is based on the shift of diffraction peaks caused by lattice strain, calculating stress values by measuring changes in specific interplanar spacing. This technique is suitable for non-destructive testing and can quantitatively analyze the stress distribution on and near the surface of the coating. However, for spring steel with deep stress or complex geometries, it needs to be combined with layer-by-layer peeling or drilling techniques. For spring steel plated with colorful coatings, X-ray diffraction can effectively identify the stress gradient at the coating-substrate interface, revealing the distribution of thermal stress caused by differences in thermal expansion coefficients, providing a basis for optimizing the coating process.
Raman spectroscopy detects stress by analyzing changes in the vibrational modes of coating molecules, and is particularly suitable for amorphous or microcrystalline coatings. When a coating is subjected to stress, the vibrational frequencies of molecular bonds shift. The magnitude of the stress can be estimated by measuring changes in Raman peak positions. This technique is sensitive to micro-stress on the coating surface and can be combined with microscopic imaging to achieve stress mapping, revealing localized stress concentration phenomena. For spring steel plated with colorful coatings, Raman spectroscopy can assist in analyzing the correlation between coating composition and stress. For example, the stress distribution differences caused by variations in elemental doping in different colored coatings provide microscale data support for coating design.
Nanoindentation technology measures the elastic recovery and plastic deformation behavior of the coating under small loads and calculates localized stress using stress-strain curves. This technique can assess the adhesion strength and stress transfer mechanism at the coating-substrate interface, revealing the impact of interfacial stress distribution on the risk of coating peeling. For spring steel plated with colorful coatings, nanoindentation can quantitatively analyze the relationship between coating hardness, elastic modulus, and stress. For example, high-hardness coatings may lead to stress concentration due to increased brittleness, while low-elastic-modulus coatings may alleviate interfacial stress through deformation, providing a basis for coating material selection.
The optical curvature measurement system monitors changes in substrate curvature after coating deposition and calculates film stress using the Stoney formula. This technology is suitable for rapid stress screening of large-area coatings, especially for stress detection on flexible substrates or complex-shaped spring steel. For spring steel plated with colorful coatings, optical curvature measurement can monitor stress evolution in real time during coating deposition, and combined with temperature control to optimize process parameters, reducing the impact of thermal stress on coating quality. Furthermore, this technology can be combined with finite element simulation to verify the accuracy of stress predictions from theoretical models, improving the reliability of coating design.
Comprehensive detection and analysis require the integration of multiple techniques to fully assess the stress state of spring steel plated with colorful coatings. For example, X-ray diffraction and Raman spectroscopy can reveal stress distribution at macroscopic and microscopic scales, respectively, while nanoindentation and optical curvature measurement can supplement interfacial stress and process stress data, constructing a complete picture of stress distribution through multi-scale data fusion. Ultimately, the test results need to be combined with the actual working conditions of the spring steel to assess the impact of stress on fatigue life, corrosion resistance, and functional stability, providing a scientific basis for coating process optimization, material selection, and structural design, and ensuring the long-term reliable operation of spring steel plated with colorful in complex environments.
