The Master’s thesis deals with the technology of surface hardening by laser. High power diode laser is used for this purpose. Surface hardening is performed on cast iron BS 1452-77, at different speeds laser head and laser power. In introduction, the theoretical part deals with possible ways of hardening focusing on the benefits of laser hardening. There are mentioned basic parts of laser, type industrial lasers and their application in industry. The final part is mentions the using of material and methods used to evaluate samples. The practical part describes the using devices and carries out evaluation macrostructure and microstructure and evaluation of hardness depending on the distance from the surface.

Yes / Aluminium alloys are widely used structural materials in automotive, aerospace, and transportation, among several other notable industries. However, aluminium alloys' low hardness and poor tribological performance prevent potential use in applications requiring high contact pressures and wear resistance. This paper presents a novel two-step technique for enhancing the mechanical properties of the aluminium alloy by impregnating the surface with Ni-coating containing hard TiO2 nanoparticles using a high-intensity electric arc generated during tungsten inert gas welding. The results show that the process significantly changes the Microstructure and mechanical properties. The surface hardness increased from 0.48 GPa to 0.65 GPa with a corresponding change of Young's modulus from 15 GPa to 24 GPa of the treated surface.

<p> Flexible manufacturing systems and lean production philosophies are in increasing industrial demand. Multiple manufacturing processes integrated into stand alone automated equipment can be utilized to greatly reduce operation costs. New technologies are continually being developed that can be easily combined with related manufacturing processes. Flexible machining and surface hardening operations can be realized in a single set-up by integrating a high-power diode laser (HPDL) within a machine tool structure.</p> <p> The following research presents the concept of integrated laser surface hardening within a machine tool environment. Experimental work was performed using a HPDL for transformation hardening of AISI 4140 steel.</p> <p> Both quasi-steady analytical and transient finite element heat transfer models have been developed. Solutions of the models are compared, which show that the more sophisticated finite element modeling is necessary only if accuracy of peak surface temperature is important. Otherwise, the simpler but faster analytical model can be used to describe the temperature profiles during laser heating.</p> <p> A novel approach using temperature indicating lacquers was shown to be a simple and reliable tool for temperature measurement. The analytical model was further used to find a best fit with the experimental measurements to estimate the fraction of laser power absorbed by the workpiece surface. With the aid of the model, it was shown that the austenite transformation temperature is highly dependent on the scanning speed. For slower speeds, the transform temperature was closer to the A3 temperature given by the iron-iron carbide phase diagram. Tests performed at faster scanning speeds indicated transformation temperatures as high as 1230 °C.</p> <p> Experiments were divided into three series. The first series was performed at slow scanning speeds (200-1000 mm/min) and low laser powers (200-500 W). Hardening was executed on flat workpieces with the laser scanning along a linear path. The second and third test series were performed at fast scanning speeds (2000-8000 mm/min) and higher laser powers (1000-2000 W) with hardening done on rotating cylindrical workpieces. The third tests series consisted of two laser passes in an attempt to increase the penetration depth of the hardened layer. These tests resulted in severe distortion due to melting that would require nearly the entire hardened layer to be machined away post heat treatment. However, if the melting temperature is not significantly exceeded multiple laser passes could be used to increase the thickness of the hardened layer.</p> <p> Higher case depths were realized for the slow tests since these tests have a greater laser-work interaction time. During laser treatment, the uncoated workpieces were left exposed to allow for oxidation and melting in order to increase the fraction of absorbed laser power. The absorptivity is shown to be as high as 85% for these tests.</p> <p> Results are presented in a form useful in selection of laser power and scanning speed to obtain the desired level of hardening, without having to resort to complex analytical or numerical models. Investigations into in-process monitoring show that measurement of surface temperature using an infrared thermometer could be used to control the generated hardened layer reducing process scrap.</p> / Thesis / Master of Applied Science (MASc)

Ce travail de thèse, porte sur le développement d’une technique originale de traitement de surface par jet d’azote cryogénique. Ce procédé a été initialement développé pour le décapage et le nettoyage des surfaces. Il est ici utilisé pour obtenir un durcissement superficiel sans altération ou endommagement de la surface du matériau traité. Sous certaines conditions, dans un premier temps, nous avons appliqué la technique jet d’azote en conditions statiques de traitement afin de cartographier les domaines d’utilisation du jet en fonction des paramètres de procédé (distance de tir et temps d’exposition). On montre, un durcissement superficiel sans endommagement de la surface du matériau cible (acier austénitique AISI 316L). L’influence de la distance à laquelle la surface est traitée (distance de tir) et le temps d’exposition du jet sur l’évolution de la microstructure, le durcissement et l’endommagement en surface de l’acier AISI 316L a été étudiée. Des analyses par microscopie électronique à balayage, des analyses d’images ainsi que des mesures de microdureté ont été effectuées sur les microstructures des surfaces traitées pour quantifier les effets de traitement par jet d’azote. Le durcissement en surface, du essentiellement à la transformation martensitique, est ainsi quantifié selon les conditions d’essai. Dans un second temps, un traitement en conditions cinématiques a été réalisé en vue d’obtenir un durcissement superficiel sans endommagement de matière. Les essais de traitement en conditions cinématiques ont été essentiellement réalisés sur les surfaces d’aciers austénitiques instables, l’AISI 316L et l’AISI 304L et, ponctuellement sur l’acier stable, l’AISI 310s. L’influence de la vitesse d’avance du jet et la pression de consigne sur l’évolution de la microstructure, les fractions de martensites formées et le niveau de durcissement en surface d’aciers AISI 316L et AISI 304L ont été étudiées. Les analyses EBSD, MEB ainsi que les mesures de microdureté réalisées sur les surfaces traitées ont permis de mettre en évidence le lien entre le niveau de durcissement et la quantité de martensite induite. Le durcissement de la surface de l’acier AISI 310s, qui reste très faible comparé à celui d’aciers instables, est le résultat de l’écrouissage de sa phase austénitique. Il a été également montré qu’un traitement avec un double passage du jet conduit à l’amélioration de la microdureté en surface des trois aciers traités / This work focuses on the study of an original surface treatment technique that uses supercritical cryogenic nitrogen jet. This process was initially designed for environmentally friendly surface cleaning, where indeed such gas recycles in the air after operation. In the present work, this technique is implemented for surface hardening use without damage of the surface to be treated. Two types of operation cases are studied: static jet tool impingement, cinematic using jet tool scanning on the top surface. In fact, these two static and cinematic treatment cases can be used in industrial operations. In the first stage, the treatment was performed under static conditions in order to map the domains of use of the process. Variation of the experimental parameters (standoff distance and dwell time - treatment time-) made possible to define several uses of the nitrogen jet. In particular the hardening without any damage of the surface of the material to be treated such as AISI 316L stainless steel. Thus, the influence of the standoff distance and the dwell time on the evolution of surface microstructure and damage and hardening was studied. To quantify the effects of nitrogen jet on the microstructure, SEM (Scaning Electrons Microscope) observations and micro hardness measurements were carried out on the treated surfaces. As a result, for different conditions of treatment, the relationship between hardness and martensite rate during surface transformation process, is shown and plotted. Secondly, we focus on hardening without surface damage. The treatments were essentially carried out on both AISI 316L and AISI 304L metastable stainless steels. The influence of both torch velocity and jet static pressure on the variation of microstructure, martensite fractions and hardening level, was also studied and discussed. Thanks to both SEM/EBSD analysis and micro hardness measurements, the relationship between martensite rate and increase of hardness, is highlighted. It is also established that the treatment using several passes allows to increase the surface micro hardness without damage. Finally, it is found that, for some particular working parameters, the nitrogen jet process can also be used for surface hardening without martensitic transformation

Made available in DSpace on 2016-12-08T17:19:23Z (GMT). No. of bitstreams: 1 Marcio de Rossi.pdf: 25090067 bytes, checksum: ab7c04de669e27612ef763eb16850faf (MD5) Previous issue date: 2014-01-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho descreve o tratamento térmico superficial a laser, caracterização dos microconstituintes e perfis de dureza obtidos no ferro fundido cinzento classe NBR FC 250. Foram variados os parâmetros de potência (300w, 400w, 500w e 600w) e velocidade de varredura (100mm/s, 20mm/s, 10mm/s, 5mm/s, 3,5mm/s e 2mm/s). Os parâmetros constantes utilizados foram diâmetro feixe do laser 8,18mm e sem sobreposição das trilhas do laser. As amostras foram caracterizadas após tratamento térmico superficial através de microscopia óptica, microscopia eletrônica de varredura e microdureza Vickers. A profundidade da camada refundida das amostras apresentou valores crescentes com a energia, para a profundidade da ZTA (camada temperada) relação com a energia incidida não foi observada. Dos resultados obtidos verificou-se que a têmpera superficial sem refusão no ferro fundido cinzento FC250 ocorre em uma faixa bem restrita, sendo que através dos parâmetros de tratamento térmico utilizados neste trabalho foi possível determinar linhas de tendência para obtenção de tal condição. Os parâmetros utilizados no tratamento térmico superficial a laser das amostras K (500w, 5mm/s), L (600w, 5mm/s), N (400w, 2mm/s) , O (500w, 2mm/s), P (600w, 2mm/s), X (500w, 3,5mm/s), Z (600w, 3,5mm/s), foram os que se obtiveram transformação de fase e consequentemente endurecimento superficial. Os parâmetros de tratamento térmico utilizados nas amostras K e N foram suficientes para promover têmpera superficial no ferro fundido cinzento, sendo que se observou 6 microestrutura martensítica refinada nestas condições. Nas amostras K e N obteve-se microdurezas superficiais de 800HV e 600HV respectivamente, sendo estes valores de microdureza superficial superior as amostras refundidas. Os parâmetros de tratamento térmico utilizados nas amostras L, X, Z, O, P promoveram refusão no ferro fundido cinzento, sendo que nestas condições foi observado microestrutura ledeburítica na região refundida, com presença de austenita retida entre a região refundida e a zona termicamente afetada (região temperada). A presença de ledeburita e austenita retida na superfície após tratamento térmico das amostras L, X, Z, O, P implicaram em menores durezas superficiais, porém nestas condições obteve-se maior profundidade de endurecimento quando comparada as amostras K e N.

This master thesis deals with surface hardening of steels, especially with rotary flash hardening of 42CrMo4 steel (WNr 1.3563, ČSN 15142). In this method homogenous heating of whole surface occurs during a very fast rotation of the component. In the theoretical part of this thesis the most common methods of surface hardening are described, with focus on laser and electron beam technologies. In the experimental part special device for this application was constructed. Rotary flash hardening was done using different radiation source and experimantal device parameters. The hardened surface layer of maximal thickness of 0,7 mm and width of 5,6 mm was achieved using laser beam. Results with electron beam were way better, because this technology allows to control the distribution of power along the beam width in order to improve the width/thickness ratio of hardened layer. Using this method maximal layer thickness of 1,4 mm and width of 13,4 mm was achieved.

The diploma thesis addressed the issue of laser surface hardening using dynamic oscillation of the laser beam. The theoretical part presents the hardening technology and suitable using of laser equipments. The fiber laser YLS 2000 was used in the experiment and the hardened material was steel 12 050, which is suitable for laser hardening. The influence of two selected parameters of the scan head on the resulting structure and hardness of hardening layers was examined. Based on the results, the choice of optimal parameters for identical conditions with the experiment was recommended.

Diploma thesis is specialized in an engineering design of mobile equipment for the surface hardening. At first, overview of methods and instruments for surface hardening is introduced. Solution to the thesis is a proposial for any eventual options of contruction, appreciation and choice of a suitable option. Subsequently, particular parts of the equipment with design and check calculations are explicated. Constructional tasks were done in the SolidWorks program. Finally, an economical analysis is described.

Oil Jet Cavitation Peening in Air (OPA) is capable of inducing compressive residual stress in standard aerospace materials. This paper demonstrates the process capabilities of OPA on Al 2024-T3. Specifically, changes in the workpiece residual stress, microhardness, mass loss and surface roughness are investigated as a function of the control parameters for the system. Additionally, the paper identifies a method to monitor the process in situ through the use of high frequency acoustic emission sensors. The results indicate the OPA process is capable of generating residual stresses comparable to those of standard shot peening, up to 60% of the yield strength of the material, at similar depths, around 300 µm. Finally, the acoustic emission signal may be utilized to monitor the process, specifically in predicting the microhardness and mass loss of the system.

Το αντικείμενο της παρούσας διατριβής είναι η ανάπτυξη μεθοδολογίας προσδιορισμού της κατανομής της σκληρότητας και του βάθους διείσδυσης της σκλήρυνσης που προκαλείται σε ένα εξάρτημα το οποίο έχει υποστεί Σκλήρυνση μέσω Λείανσης (Grind-Hardening). Η διεργασία Σκλήρυνσης μέσω Λείανσης είναι μία νέα επιφανειακή θερμική κατεργασία η οποία χρησιμοποιεί την θερμότητα που αναπτύσσεται στην ζώνη λείανσης για την θερμική κατεργασία του κομματιού. Η παρούσα διατριβή επικεντρώνεται στην ανάπτυξη μαθηματικών μοντέλων ικανών να προβλέψουν τα διάφορα χαρακτηριστικά της διεργασίας (δηλ. τη τοπογραφία της επιφάνειας του λειαντικού τροχού, τις δυνάμεις κατεργασίας, την παραγωγή και τον επιμερισμό της θερμότητας και την θερμοκρασιακή κατανομή). Τα μοντέλα αυτά συνδυαζόμενα επιτρέπουν τον προσδιορισμό της κατανομής σκληρότητας και του βάθος δι-είσδυσης της σκλήρυνσης συναρτήσει των παραμέτρων της διεργασίας και των χαρακτηριστικών του λειαντικού τροχού που χρησιμοποιείται. Παράλληλα, η εφαρμογή των μοντέλων αυτών οδηγεί σε χρήσιμα συμπεράσματα σχετικά με τα όρια εφαρμογής της διεργασίας. Μετά την επιβεβαίωση των θεωρητικών προβλέψεων, εξάχθηκε βάση δεδομένων υπολογισμού του βάθους διείσδυσης της σκλήρυνσης συναρτήσει της ροής θερμότητας στο κομμάτι και των παραμέτρων της διεργασίας. Η μεθοδολογία που αναπτύχθηκε εφαρμόστηκε για την περίπτωση σκλήρυνσης οδηγών κύλισης (raceway). Το σημαντικότερο συμπέρασμα που προκύπτει από την συγκεκριμένη διατριβή είναι ότι η διεργασία σκλήρυνσης μέσω λείανσης μπορεί να θεωρηθεί αρκετά «ώριμη» ούτως ώστε να μπορεί να εισαχθεί στην βιομηχανική πρακτική για την επιφανειακή σκλήρυνση εξαρτημάτων. Τα διάφορα χαρακτηριστικά της διεργασίας μπορούν να προβλεφθούν ενώ τέθηκαν οι βάσεις δημιουργίας ενός συστήματος παρακολούθησης και προγραμματισμού της διεργασίας. / The objective of the present study is the development of a methodology capable of predicting the hardness distribution and the hardness penetration within a grind-hardened workpiece. Grind-hardening is a novel-alternative surface hardening process that utilizes the heat generated in the grinding zone for the heat treatment of the workpiece material. The present work has employed analytical and numerical modeling techniques for describing the characteristics and output of the process, i.e. the topography of the grinding wheel, the process induced forces, the heat generation and partition and the temperature distribution within the work-piece. These models when coupled allow the estimation of the hardness distribution and the hardness penetration depth as a function of the process parameters and the characteristics of the grinding wheel. Additionally, through the process modeling, the process limitations are identified. After proving the validity of the theoretical predictions, the coupled models were utilized for the extraction of a data base providing the hardness penetration depth as a function of the heat flow entering the workpiece and the process parameters. The developed methodology was used for programming the grind-hardening of raceways. The main conclusion of this work is that grind-hardening process can be nowadays introduced in the industrial practice. The methodology developed, allows the prediction of the process outcome and can be used in the future for setting up an on-line monitoring system and / or develop an off-line process programming system.