Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less.

Ultrasonic flaw detection spectrogram characterization of vermicular graphite cast iron engine cylinder head

The defects formed in the manufacture of the vermicular graphite cast iron engine cylinder head seriously affect the operation of the engine, which is necessary to detect. Ultrasonic testing is a non-destructive testing method that has the advantages of quick response, high resolution, and high security. In this paper, various types of specimens are prepared corresponding to different types of actual defects in the vermicular iron cylinder head. An ultrasonic A-scan system was built to test the specimens. The short-time Fourier transform, the continuous wavelet transform, the empirical wavelet transform, and the empirical modal decomposition were adopted to transform the signals into spectrograms which were further analyzed to reveal the inherent features of defects. The results show that the short-time Fourier transform can be used to distinguish all the common defects comparing to other methods. Comparing to the time-domain waveforms, the transformed spectrograms provide clear time-frequency distribution and highlight the inherent characteristics of the signal.

CORRELATION BETWEEN CUTTING TEMPERATURES AND METALLURGICAL PROPERTIES OF COMPACTED GRAPHITE CAST IRONS IN THE END MILLING PROCESS

In the search for more energy-efficient internal combustion engines, the automotive companies keep pushing the working temperatures and pressures of the engines, leading to more extreme working conditions and so the necessity of new materials. Among the most promising materials for the new generations of engines is the compacted graphite cast iron, which is more wear-resistant than aluminum and tougher than gray cast iron. However, this combination of properties also leads to decreased machinability, increasing production costs and, therefore, their market competitiveness. This paper evaluated the correlation of mechanical and metallurgical properties and the cutting power and surface roughness of three grades of compacted graphite cast iron with the cutting temperature in the end milling process under different two different feed rates and cutting speeds. This analysis showed that the temperatures near the cutting zone are closely correlated to the material's mechanical properties, machining power, and resulting roughness. These results indicate that thermographic images are a good indicator of the overall correlation between the changes in material properties and the most usual machinability output parameters.

ANALYSIS AND THERMODYNAMIC STABILITY OF NUCLEI IN SPHEROIDAL GRAPHITE IN Fe–C–Si ALLOYS

The paper describes the graphite nuclei constitution for spheroidal graphite cast iron melted in a cupola furnace, which is treated by the addition of magnesium and inoculated with a barium-based inoculant. Two samples of spheroidal cast iron were analysed, differing only in tin content. Field-emission scanning electron microscopy (FE -SEM) with energy-dispersive X-ray spectroscopy (EDS) was used to analyse the nuclei. The thermodynamic calculation of the phase equilibria and the associated free formation energies of the alloys were calculated and compared with metallographic observations. It was found that the nuclei in the spheroidal graphite are different in shape and composition. Spherical and rectangular ones were found, and in many cases the porosity was present at the nuclei. The nuclei consisted of different compounds such as (Mg,Ca)S, MgO, (Mg,Al,Si)N. The amount of Sn only affected the pearlite content, and there were no Ba and rare earths present in the nuclei.

Influence of Austempering Temperatures on the Microstructure and Mechanical Properties of Austempered Ductile Cast Iron

The influence of the austempering temperatures on the microstructure and mechanical properties of austempered ductile cast iron (ADI) was investigated. ADI is nodular graphite cast iron, which owing to higher strength and elongation, exceeds mechanical properties of conventional spheroidal graphite cast iron. Such a combination of properties is achieved by the heat treatment through austenitization, followed by austempering at different temperatures. The austenitization conditions were the same for all the samples: temperature 890 °C, duration 30 min, and quenching in a salt bath. The main focus of this research was on the influence of the austempering temperatures (270 °C, 300 °C, and 330 °C) on the microstructure evolution, elongation, toughness, and fatigue resistance of ADI modified by certain amounts of Ni, Cu, and Mo. The Vickers and Rockwell hardness decreased from 535.7 to 405.3 HV/1 (55.7 to 44.5 HRC) as the austempering temperature increased. Optical images showed the formation of graphite nodules and a matrix composed of ausferrite; the presence of these phases was confirmed by an XRD diffraction pattern. A fracture surface analysis revealed several types of the mechanisms: cleavage ductile, transgranular, and ductile dimple fracture. The stress-controlled mechanical fatigue experiments revealed that a 330 °C austempering temperature ensures the highest fatigue life of ADI.

Mid-Layer Visualization in Convolutional Neural Network for Microstructural Images of Cast Irons

We attempted to classify the microstructural images of spheroidal graphite cast iron and grey cast iron using a convolutional neural network (CNN) model. The CNN comprised four combinations of convolution and pooling layers followed by two fully-connected layers. Numerous microscopic images of each cast iron were prepared to train and verify the CNN model. After training the network, the accuracy of the model was validated using an additional set of microstructural images which were not included in the training data. The CNN model exhibited an accuracy of approximately 98% for classification of the cast irons. Typically, CNN does not provide bases for image classification to human users. We tried to visualize the images between the network layers, to find out how the CNN identified the microstructures of the cast irons. The microstructural images shrank as they passed the convolutional and pooling layers. During the processes, it seems that the CNN detected morphological characteristics including the edges and contrast of the graphite phases. The mid-layer images still retained their characteristic microstructural features, although the image sizes were shrunk. The final images just before connecting the fully-connected layers seemed to have minimalized the information about the microstructural features to classify the two kinds of cast irons. Matrix phases such as ferrite and pearlite did not show prominent effects on the classification accuracy.