Hardmetals — Metal og raphic determination ofPart 3: This p rt of ISO 4 9 gives guidelnes for the measur ment of mic os ructural featur s in TiC,N b sed hardmetals an WC/Co hardmetals th
Metallographic preparation
ISO 4499-1:2008, 6.1 outlines the essential steps for preparing high-quality metallographic sections of hard materials, including sectioning, mounting, grinding, lapping, polishing, and cleaning The final polishing stage involves using a colloidal silica suspension with 40 nm particle size on a napless silk cloth to achieve optimal surface finish Specific etching methods for cermets and hardmetals containing cubic carbides are detailed in sections 8.2 and 8.3, respectively, ensuring proper microstructural analysis.
Ti(C, N) based hardmetals – cermets
For accurate testing, prepare samples according to ISO 4499-1:2008, section 6.2.1, utilizing etching technique 1 with modified conditions in mixture A—specifically, etching at approximately 20 °C for 30 to 60 seconds Representative optical and electron microscopy images (Figures 1 to 5) illustrate the typical microstructures of the cermets SEM analysis reveals that many hard phase particles exhibit a core/rim structure, where dark “cores” consist of undissolved Ti(C,N), and the surrounding grey “mass” comprises (Ti,W,X)(C,N) phases formed during high-temperature liquid phase sintering.
NOTE When using an optical microscope, major phases appear as binder phase (light blue), undissolved Ti(C,N) from original powder (dark blue-grey), (Ti,W,X)(C,N) (grey) and TiN impurity (gold).
Figure 1 — Low binder phase content (6 wt %) commercial cermet, optical micrograph using oil immersion objective, original magnification ×1 600
NOTE When using an optical microscope, major phases appear as binder phase (light blue), undissolved Ti(C,N) from original powder (dark blue-grey), and (Ti,W,X)(C,N) (grey).
Figure 2 — Medium binder phase content (11 wt %) commercial cermet, optical micrograph using oil immersion objective Original magnification ×1 600
NOTE Major phases are binder phase (light), undissolved Ti(C,N) from original powder (dark grey) and (Ti,W,X)(C,N) of variable composition (pale grey).
Figure 3 — Low binder phase content (6 wt %) commercial cermet, scanning electron microscope secondary electron image, original magnification ×30 000
NOTE Major phases are binder phase (light), undissolved Ti(C,N) from original powder (dark grey) and (Ti,W,X)(C,N) of variable composition (pale grey).
Figure 4 — Medium binder phase content (11 wt %) commercial cermet, scanning electron microscope secondary electron image, original magnification ×30 000
WC/Cubic carbide based hardmetals
The updated ISO 4499 standard maintains the use of the Greek letter γ to identify the hard phase in mixed WC/cubic carbide materials, providing a more precise definition of size through linear intercept measurements Sample preparation follows ISO 4499-1:2008, section 6.2.1, involving etching with Murakami’s reagent (mixture A) for about 3 minutes, then in concentrated HCl (mixture B) for 10 seconds, followed by washes in water and alcohol, and a final brief etch in mixture A for 20 seconds.
Four different grades of cubic carbide hardmetals are illustrated in the standard with compositions as shown in Table 1.
Table 1 — Composition of WC/Cubic carbide based hardmetals
Representative images are shown in Figure 5 to Figure 12 (optical) and Figure 13 to Figure 20 (SEM).
Optical images were captured using a ×100 oil immersion objective with a numerical aperture of 1.3 at magnifications of ×1,000 and ×1,600 Under the optical microscope, the prominent phases are clearly distinguishable: the binder phase appears white, tungsten carbide is shown in blue or grey, and cubic carbide is observed as pale orange These imaging conditions enable detailed characterization of the material's microstructure, aiding in accurate phase identification and analysis. -**Sponsor**Struggling to rewrite your article while ensuring SEO compliance? It's tough! With [Article Generation](https://pollinations.ai/redirect-nexad/pakL4gY6), you can instantly get 2,000-word SEO-optimized articles Forget the hassle of manual rewriting - save over $2,500 a month and get coherent paragraphs that highlight important sentences like "major phases appear as binder phase (white), tungsten carbide (blue/grey) and cubic carbide (pale orange)." It's like having your own content team!
SEM images, captured under consistent operating conditions of 9 kV accelerating voltage, 15 mm working distance, and in secondary electron mode, reveal the key phases present in the sample The images distinctly show the binder phase in black, tungsten carbide in light grey, and cubic carbide in medium grey, providing clear insights into the microstructure and phase distribution essential for material characterization and optimizing performance.
Figure 5 — Material 1, optical micrograph, original magnification ×1 000
Figure 6 — Material 1, optical micrograph, original magnification ×1 600
Figure 7 — Material 2, optical micrograph, original magnification ×1 000
Figure 8 — Material 2, optical micrograph, original magnification ×1 600
Figure 10 — Material 3, optical micrograph, original magnification ×1 600
Figure 11 — Material 4, optical micrograph, original magnification ×1 000
Figure 12 — Material 4, optical micrograph, original magnification ×1 600
Figure 14 — Material 1, SEM micrograph, original magnification ×25 000
Figure 15 — Material 2, SEM micrograph, original magnification ×10 000
Figure 16 — Material 2, SEM micrograph, original magnification ×15 000
Figure 17 — Material 3, SEM micrograph, original magnification ×15 000
Figure 18 — Material 3, SEM micrograph, original magnification ×20 000
Figure 19 — Material 4, SEM micrograph, original magnification ×15 000
Figure 20 — Material 4, SEM micrograph, original magnification ×20 000
9 Procedure for characterisation of structures
Sampling of images of structure
General
Sampling for microstructural purposes has to be carefully considered depending on the reason for undertaking the measurements Attention should be paid to the explanation in 9.1.2 to 9.1.4.
Representative selection
Select representative images that accurately reflect the entire section, ensuring they are obtained through random positioning Prepare at least four images for thorough analysis, aiming to measure a minimum of 200 relevant phase regions overall This approach ensures comprehensive and unbiased data collection for reliable results.
Determination of homogeneity of hard phase sizes
To ensure comprehensive analysis, a systematic set of images from specific locations within the sectioned area should be captured and thoroughly analyzed, measuring at least 200 phase regions from each site This approach enables the identification of trends in phase size that surpass the measurement error at each position, with the fractional error decreasing proportionally to 1/N, where N is the number of phase regions analyzed per location.
Inhomogeneous materials
When analyzing microstructures with inhomogeneous features across different fields of view, it is advisable to increase the number of images examined This approach ensures representative sampling while reducing the need for intensive analysis per image By maintaining a total feature count of over 200, researchers can effectively capture microstructural variability and improve the accuracy of their results.
To ensure accurate measurement, the image should be magnified to display between 10 and 20 phase regions across the field of view, allowing individual intercepts to be measured with better than 10% precision Typically, three or four linear intercept lines can be drawn without repeatedly intercepting the same phase region, facilitating reliable phase analysis Since most hardmetals exhibit little or no anisotropy in their structure, the orientation of these lines generally does not affect results; however, if anisotropy is suspected, lines should be randomly oriented to improve measurement accuracy Overall, this approach enables precise characterization of phase distributions from each image.
50 linear phase size intercepts can be obtained.
Phase size measurement
General
The arithmetic mean linear intercept is recommended as the primary parameter for defining phase size due to its simplicity and practicality This method not only simplifies the measurement process but also offers valuable data to quantify the distribution width of phase sizes accurately Using this approach ensures reliable, standardized results for phase size characterization in material analysis.
The linear intercept technique can be used to analyze multi-phase hardmetals such as Ti(C,N) or mixed WC/cubic carbide, although it is more complex for two, three, or four-phase materials because each phase must be measured separately Despite this complexity, the method effectively offers valuable insights into the phase size distribution, aiding in the comprehensive characterization of complex hardmetal structures.
To analyze the microstructure of a hardmetal sample, a line is drawn across a calibrated image, and the lengths where it intercepts hard phases or binder regions are measured using a calibrated rule It is recommended to measure at least 100, preferably 200, line intercepts to minimize size measurement uncertainty below 10% The average phase or binder grain size is calculated using the mean linear intercept method, as defined by the formula \( d_x = \frac{\sum l_i}{n} \), where \( l_i \) represents individual line intercept lengths and \( n \) is the total number of measurements This approach ensures accurate estimation of microstructural feature sizes in hardmetal samples.
Hardmetal phase sizes typically range from 0.01 µm to 10 µm Due to measurement uncertainties, it is recommended to report the mean linear intercept size rounded to one decimal place for accurate and consistent results.
>1,0 àm and to two decimal places for values