Hardening Efficiency and Microstructural Changes during Laser Surface Hardening of 50CrMo4 Steel

Laser surface hardening is an attractive heat treatment solution used to selectively enhance the surface properties of components by phase transformation. A quantitative parameter to measure the efficacy of hardening processes is still lacking, which hinders its application in industries. In this paper, we propose a simple approach to assess the effectiveness of the process by calculating its thermal efficiency. The proposed method was applied to calculate the hardening efficiency during different laser processing conditions. This study revealed that only a small portion of supplied laser energy (approximately 1–15%) is utilized for hardening. For the same laser system, the highest efficiency is achieved when surface melting is just avoided. A comparative study showed that pulsed lasers are more efficient in energy utilization for hardening than continuous wave laser. Similarly, the efficiency of a high-power laser is found to be higher than a low-power laser and an increase in beam absorption produces higher hardening efficiency. The analysis of the hardened surface revealed predominantly martensite. The hardness value gradually decreased along the depth, which is attributed to the decrease in percentage of martensite.

The Determination of Priority Areas for the Construction of Green Roofs with Use of the Urban Area Valorisation Method

The aim of the research was to valorise the analysed urbanized area in the direction of determining the hierarchy in the order of interventions aimed at increasing the share of biologically active area and natural field retention, the potential impact of green roofs on the valorisation of the studied urbanized areas. The research covered the Gajowice estate in Wrocław. The scope of the research included the division of the area into working cells, for which valorisation was carried out using the point method based on the criterion of the degree of covering the land with vegetation and the degree of covering the area with various types of buildings. The valorisation result was determined on the basis of a comparative matrix taking into account the results of the partial assessment of vegetation and building cover. The impact of green infrastructure (green roofs) on valorisation was simulated by proposing their location on buildings with the so-called big plate. The introduction of green roofs on selected buildings improved the valorisation result in some research cells, reducing the number of cells requiring intervention. This raised the valorisation assessment by even two classes, which resulted in a significant reduction in the number of critical areas, with too much hardened surface, and increased the number of areas with a satisfactory level of biologically active surfaces.

Getting wear-resistant coatings on aluminum alloys by laser alloying

A method to improve the properties of aluminum alloys by laser surface alloying is considered. The optimal selection of alloying elements is carried out. It is shown that this method of hardening increases the wear resistance and reduces the friction ratio of the hardened surface.

Microcracks Reduction in Laser Hardened Layers of Ductile Iron

A study of surface hardening of Ductile Iron (DI) with and without austempering heat treatment was developed. The chemical composition of the material contains alloying elements such as Cu and Ni, that allow to obtain a Ductile Iron Grade 120-90-02, based on ASTM A536, which was heat treated to be transformed to Austempered Ductile Iron (ADI). Specimens of 10 × 10 × 5 mm3 were obtained for application of surface hardening by Nd:YAG UR laser of 150 W maximum power. The parameters used were advance speed of 0.2 and 0.3 mm/s and power at 105, 120, 135 and 144 W; the departure microstructures were fully pearlitic in the samples without heat treatment, and ausferrite for austempered samples. Microstructural characterization of hardened samples was performed were analyzed and martensite and undissolved carbides were identified in the pearlitic samples, while in ausferrite samples it was found finer martensite without carbides. The depth of hardened surface to different conditions and their respective microhardness were measured. The results indicate that the surface hardening via laser is a suitable method for improving wear resistance by means of hardness increment in critical areas without compromising the core ductility of DI components, but the surface ductility is enhanced when the DI is austempered before the laser hardening, by the reduction of surface microcracks.

Mechanisms and Empirical Modeling of Evaporation from Hardened Surfaces in Urban Areas

Urban evaporation, as an essential part of local water vapor resources in urban areas, has often been underestimated. One possible reason is that the evaporation of urban hardened surfaces is seldom considered and poorly understood in urban evaporation estimation. This study focused on the mechanisms and calculation of evaporation on hardened surfaces in urban areas. Experimental monitoring was used to monitor the processes and characteristics of evaporation on hardened surfaces. Mathematical models based on water quantity constraints were built to calculate evaporation of hardened surfaces. The results showed that: The interception abilities for rainwater and rainfall days of impervious hardened surfaces determine their evaporated water amount, which means no water, no evaporation for the impervious surfaces. The greater evaporation of artificial sprinkling on roads happened in fewer days of rainfall and frost. The evaporation of pervious hardened ground is continuous compared to the impervious surface. Its soil moisture in the sub-layer of permeable concrete decreases periodically with a period of one day. The evaporation of hardened surfaces occupies 16–29% of the total amount of evaporation in the built-up areas in cities. Therefore, the hardened surface evaporation has great significance on the urban hydrological cycle and urban water balance.

Kryogenes Fräsen additiv gefertigter Bauteile/Cryogenic milling of additively manufactured components

Die erreichbare Oberflächenqualität additiv gefertigter Bauteile ist für industrielle Anwendungen häufig unzureichend. Daher ist eine in der Regel spanende Nachbearbeitung der Bauteile unumgänglich. In diesem Beitrag wird die spanende Nachbearbeitung durch eine kryogene Kühlung ergänzt. Hierdurch wird die thermische Belastung in der Werkstückrandschicht reduziert, um so eine Kaltverfestigung zu begünstigen. Es konnte eine verbesserte Oberflächenqualität sowie eine Randschichthärtung realisiert werden.   The surface quality of additively manufactured components is often insufficient for industrial applications. As a result, additional processes are necessary to improve the surface quality. In the investigations presented, a cryogenic cooling is used when milling additively manufactured components. The cryogenic cooling strategy favors the introduction of strain hardening effects into the surface layer. An improved surface quality as well as a hardened surface layer were realized.

The service life increasing of bushings by electro-acoustic spraying

The control of obtaining the predicted physico-mechanical properties of protective coatings of machine parts in a complex acoustic field by the method of electroacoustic spraying is carried out through the use of highly concentrated sources of electrical energy. The prediction of the physico-mechanical properties of the hardened surface of machine parts is made on the basis of the experiment planning methodology with non-orthogonal planning matrices. The adequacy of the obtained mathematical models was carried out using the criterion of adequacy of Fisher. Physical fundamentals of mass transfer of materials to a substrate in a complex acoustic field, realized through the transformation of longitudinal vibrations, to longitudinal-torsional, have been developed, while the amplitude of oscillation of the acoustic system is 5 to 15 micrometers. The use of longitudinal-torsional ultrasonic waveguides in this process and ultrafast cooling temperatures make it possible to form elements such as carbides, carbonitrides, and intermetallic compounds on the surface of a conductive material. The subsequent impact with a shift against the surface produced by the waveguide - electrode leads to irreversible microplastic deformations of the surface layer, which provide the specified parameters of surface quality and its physico-mechanical properties.