Feb_March_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 2 0 2 9 TECHNICAL SPOTLIGHT Fig. 1 — Phase analysis of a dual-phase polymer cross section sample. HOW TO CHOOSE THE BEST ANALYSIS METHOD FOR YOUR NEXT APPLICATION This primer discusses some important considerations when it comes to selecting the right technique for comprehensive microstructural analysis, based on the material and application. Fig. 2 — Cross section of a machined metal part showing pores in red. I nsight into the microstructure of ma- terials is important for evaluating their properties, controlling the man- ufacturing process, and predicting the material’s performance. Optical micro- scopes enable users to see beyond the capabilities of their naked eyes into the fine details of these microstructures. But a microscope is only part of what is needed. A digital microscope camera and image analysis software are used to capture and analyze themicroscope im- ages so that users can evaluate if a ma- terial meets their requirements. In this article, three related methods are ex- plored—phase analysis, porosity, and particle distribution—along with their similarities and differences. A discus- sion of robust image analysis modules now available with modern software is also included. The following techniques share certain commonalities, as they can use color, intensity, or hue-saturation- intensity value thresholding tech- niques to identify features in the sam- ple. Therefore, it is helpful to use image analysis software to acquire informa- tion quickly and efficiently. Each meth- od breaks out the data differently, so which one works best depends on the specific application. PHASE ANALYSIS Phase analysis is one of the most basic ways of identifying and sorting multiple material phases and micro- structure components. The phases, which represent different components within the material, can be automati- cally detected by the software as long as they have sufficient color or gray val- ue variation. This technique precise- ly calculates the area fraction of each component. For example, Fig. 1 shows the cross section of a dual-phase polymer. Using the phase analysis module of an image analysis program, the user can easily determine the amount of the dif- ferent phases. In this example, polymer A (gray) makes up 87.91%, and polymer B (blue) makes up 12.08%. Users can then compare this data with the desired material composition to identify wheth- er or not the synthetic process meets the quality standards. Other applica- tions well suited to this type of analy- sis include welding quality checks, die casting, and steel microstructures. The image analysis program used here, Olympus Stream software, of- fers a phase analysis module for the essentials, motions, and enterprise ver- sions. Up to 16 different phases can be defined as well as multiple regions of in- terest (ROIs). Users can choose wheth- er to run the analysis across the entire sample or restrict it to collect data only from defined ROIs. Several color spaces can be used (such as RGB or HSV) and minimal size criteria can be defined. Re- sults are expressed as phase fraction area calculations. POROSITY MEASUREMENT Many image analysis programs of- fer a porosity measurement module that calculates the area fraction and the number of pores on cross-sectional sur- faces or coatings. Initially, this function was used by manufacturers of porous materials, such as foam. Now, it is also used to check product or coating quali- ty by quantifying voids or defects in the materials. Porosity analysis starts like phase analysis but provides data that is specific to defining pores. The software uses the threshold method to differen- tiate between the pores and the sub- strate using color or gray level images.