A review of measurement methods for in-situ monitoring of directionally solidified engineering materials

Za dosego želenih fizikalnih in mehanskih lastnosti inženirskih materialov je ključnega pomena natančno spremljanje razvoja mikrostrukture pri izdelavi materialov. V prispevku je zbran pregled merilnih metod, s katerimi je mogoče kontrolirano spremljanje usmerjenega strjevanja. Predstavljene metode temeljijo na neporušnem in kontinuirnem ugotavljanju vrednosti vplivnih parametrov v bližini strjevalne fronte (▫$G_SF$▫ - temperaturni gradient na strjevalni fronti, ▫$V_SF$▫ - hitrost potovanja strjevanja fronte, ▫$deltaT_SF$▫ -podhladitev strjevalne fronte, ugotavljanje oblike stjevalne fronte) med samim usmerjenim strjevanjem in jih je mogoče uporabiti v raziskovalni in industrijski praksi.To achieve the required physical and mechanical properties of engineering materials, accurate monitoring of the microstructure evolution during the process of production is of crucial importance. This paper reviews some methods used for in-situ monitoring of the directional solidification process. Emphasis is given to the methods which allow nondestructive and online monitoring of the influence of parameters in the vicinity of the solidification front (▫$G_SF$▫ - temperature gradient on the solidification front, ▫$V_SF$▫ - velocity of the solidification front, ▫$deltaT_SF$▫ - supercooling of the solidification front, determination of the interface shape) during the directional solidification process. The methods can be used in research and in industrial applications

Characterization of directional solidification in a Cu-Cr-Zr alloy with quantitative microstructural analysis

V prispevku predstavljamo rezultate raziskovalnega dela, s katerim smo želeli preveriti možnosti določitve vplivnih parametrov pri usmerjenem strjevanju zlitin s kvantitativno analizo lite mikrostrukture. Pri vzorcih usmerjeno strjene zlitine Cu-Cr-Zr smo z različnimi metodami kvantitativne analize izmerili geometrijske parametre mikrostrukture (primarno in sekundarno dendritno razdaljo ter volumski delež evtektika) in ob upoštevanju analitičnih izrazov, ki podajajo razmerja med geometrijskimi parametri mikrostrukture ter parametri strjevanja, slednje tudi določili. Primerjava tako določenih parametrov strjevanja z eksperimentalno izmerjenimi vrednostmi je pokazala dobro ujemanje.In this paper the results of our research on tahe possibilities for defining the influencing parameters that describe a directionally solidified microstructure using quantitative microstructural analysis are presented. The geometrical microstructural parameters (primary and secondary dendrite arm spacing and the eutectic volume fraction) were measured with different methods of quantitative analysis on samples of directionally solidified Cu-Cr-Zr alloy. The solidification parameteres were then calculated considering the relations between solidification and geometric microstructural parameters. The composition shows a good agreement between the calculated solidification parameters and the solidification parameters determined by experiment

Engineering Materials

Učbenik je kot osnovna literatura namenjen študentom 1. stopnje študijskih programov Strojništvo, Gospodarsko inženirstvo in Mehatronika. Učbenik sestavljajo tri samostojna poglavja, ki kot celota prinašajo znanja s področja materialov in tehnologij in so potrebna pri razvoju, raziskavah in uporabi materialov na področju strojništva, elektrotehnike, avtomatike, energetike ... Prvo poglavje obravnava značilne skupine konstrukcijskih materialov in njihovo zgradbo. Opisani so osnovni pojmi in predstave o materialih, ki so potrebne za razumevanje njihovih lastnosti. V drugem poglavju so obravnavane ključne lastnosti konstrukcijskih materialov, ki omogočajo uspešno izbiro materialov za določeno aplikacijo. Tretje poglavje vsebuje izbrane primere konstrukcijskih materialov. Opisuje posebna jekla za uporabo v strojništvu, lahke zlitine, konstrukcijsko keramiko, keramična stekla in polimerne materiale.The textbook is intended as a basic literature, for students of the 1st level of the study programs Mechanical Engineering, Industrial Engineering and Mechatronics. The textbook consists of three independent chapters, which as a whole bring knowledge in the field of materials and technologies and are needed in the development, research and use of materials in mechanical engineering, electrical engineering, automation, power industry ... The first chapter deals with typical groups of engineering materials and their structure. The basic concepts and facts about materials needed to understand their properties are described. The second chapter discusses the key properties of engineering materials that enable the successful selection of materials for a particular application. The third chapter contains selected examples of engineering materials. It describes special steels for use in mechanical engineering, light alloys, engineering ceramics, ceramic glasses and polymer materials

Influence of metal surface finishing on porcelain microstructure failures in porcelain-fused-to-metal dental restoration

Čeprav je sodobni trend v fiksni protetiki v uporabi polnokeramičnih zobnih nadomestkov, so raziskave pokazale, da se še vedno najpogosteje uporabljajo kovinsko-porcelanski zobni nadomestki. Namen v tem prispevku predstavljene raziskave je ugotoviti, kako različne tehnike mehanske obdelave površine kovinskega ogrodja vplivajo na pojav napak v porcelanskem sloju ter mejni površini kovina-porcelan. V okviru izvedenih raziskav smo izdelali vzorce iz Co-Cr zlitine z različnimi metodami in tehnikami površinske obdelave. Sledila je priprava metalografskih obrusov s pomočjo katerih smo analizirali vpliv površinskih obdelav na spremembo makro- in mikrostrukture kovinskega ogrodja, porcelanskega plašča in mejne površine med njima. Rezultati opravljenih raziskav so pokazali, da je pojav napak pri vzorcih katerih kovinsko ogrodje je bilo obdelano z brusnim sredstvom v eni smeri minimalen, površina kovinskega ogrodja enakomerno hrapava z enakomerno povprečno debelino oksidne plasti 3,5µm. Pri vzorcih s kovinskim ogrodjem obdelanim z brusnim sredstvom v več smereh, smo opazili bolj hrapavo površino kovinskega ogrodja s prisotnostjo plastične deformacije površine kovinskega ogrodja, ki tvori tanjšo oksidno plast.Although the current trend in fixed prosthetics is the use of full-ceramic dental restorations, research has shown that most commonly used are still metal-ceramic dental restorations. The purpose of the research presented in this paper is to find out how different techniques of mechanical treatment of the surface of the metal frame affect the occurrence of defects in the porcelain layer and the metal-porcelain interface. As part of the research, we produced samples from Co-Cr alloy using various surface treatment methods and techniques, followed by the preparation of metallographic tablecloths, with the help of which we analyzed the influence of surface treatments on the change in the macro- and microstructure of the metal framework, the porcelain veneer and the interface between them. The results of the conducted research showed that the occurence of defects in samples whose metal surface was treated with an abrasive in one direction is minimal, the surface of the metal framework is uniformly rough with an average thickness of the oxide layer of 3,5µm. In samples with a metal framework treated with an abrasive in several directions, we observed a rougher surface of the metal framework with the presence of plastic deformation of the surface of the metal framework, which forms a thinner oxide layer

Monitoring of the eutectic Pb-Sn alloy during directional solidification

Formiranje mikrostrukture med strjevanjem, ki je odvisno predvsem od hitrosti strjevalne fronte vSF in temperaturnega gradienta GSF v njeni bližini, močno vpliva na mehanske in druge lastnosti lite zlitine. Zato je za doseganje želenih lastnosti strjenih zlitin potrebno poznanje odvisnosti med vplivnimi parametri strjevanja ter nastajajočo mikrostrukturo. Merilne metode, ki omogočajo sprotno in neporušno spremljanje teh parametrov že v fazi formiranja mikrostrukture, so velik izziv pri razvoju modernih inženirskih materialov. V prispevku obravnavamo možnosti uporabe sprotnega merjenja spremembe električne upornosti med usmerjenim strjevanjem za določitev položaja in hitrosti strjevalne fronte vSF. Spremembo električne upornosti smo merili med usmerjenim strjevanjem vzorca evtektične zlitine Pb-Sn pri različnih hitrostih pomika vzorca iz grelne cone ter konstantnem temperaturnem gradientu peči. Tako dobljene vrednosti hitrosti strjevalne fronte vSF smo primerjali s tistimi, ki smo jih določili pri enakih pogojih strjevanja z meritvijo spremembe temperature s termočleni, nameščenimi v notranjosti vzorca.Microstructure evolution during solidification primarily depends on the velocity vSF and the temperature gradient GSF of the solidification front. It has a great influence on the mechanical and other properties of the cast alloys. It is therefore important to know the relationship between the influential solidification parameters and the evolving microstructure if the desired properties of solidified alloys are to be achieved. Thus, the measurement methods that allow online and nondestructive monitoring of these parameters represent a great challenge in the evolution of modern engineering materials. In this paper we discuss the usability of in-situ measurements of electrical resistance changes during the directional solidification for tracing the position and the velocity of the solidification front vSF. The electrical resistance changes were measured during directional solidification on a sample of the Pb-Sn eutectic alloy at different pulling velocities for displacing samples from the heating zone and at a constant temperature gradient of the furnace. The obtained values of the solidification front velocities vSF were subsequently compared with the values determined during the same solidification conditions by measuring the temperature changes with thermocouples, placed inside the sample

Monitoring of directional solidification with simultaneous measurements of electrical resistance and temperature

WE present the efficiency of simultaneous electrical resistance and temperature (ERT) measurements for monitoring the position, X, and the growth rate, V, of the solidification front during the directional solidification of alloys. On alaboratory device for directional solidification (Bridgman-type furnace), theeutectic Pb-Sn alloy was solidified at five different pulling rates, VP, with a constant imposed temperature gradient, GP. During directional solidification, the electrical resistance and the temperature changes were measured simultaneously in the experimental samples. The results of the experiments show that simultaneous measurement of ERT enables not only the determination of the average growth rate, V, during directional solidificationbut also its fluctuation over the total measurement length of the sample

In-situ monitoring of internal oxidation of dillute alloys

This paper presents a non-destructive measurement method that enables identification and characterization of phenomena during internal oxidation of metallic materials as well as monitoring the kinetics of internal oxidation using "in-situ" electrical resistance measurements. A special laboratory device, based on the unique measurement cell, for the electrical resistance measurements at high temperatures and the model for electrical resistance transformation into an instantaneous microstructure were developed. To accomplish this, the process of internal oxidation was divided into the sequence of the key partial reactions that were presented in the model as the parallel andžor serial connected time variable resistors in the electrical circuit. The validity of the transformation model was experimentally confirmedby internal oxidation of Ag-Sn (2 at.% Sn) alloy at different oxidation temperatures in air atmosphere. The comparison of the results obtained by "in-situ" electrical resistance measurements with those obtained by metallographic analysis and Wagnerćs theory shows that the novel method presents a more effective tool for monitoring of internal oxidation kinetics. The method identifies also the microstructural defects and their influences onthe kinetics of internal oxidation

Untersuchung der Mikrostruktur schmelzgesponnener Bänder auf NiTi-Basis

In order to get small-dimensioned shape memory alloys (SMAs) with good functional and mechanical properties, a rapid solidification technique was employed. This paper discusses the use of different melt-spinning procedures for the preparation of proper thin NiTi ribbons. Metallographic characterization of SMAs is an important way to evaluate material properties, therefore the effect of alloy composition and different conditions of melt-spinning process (crucible, melting time and temperature) on the various inclusions and microstructure of NiTi alloys was investigated. Specimens for metallographic studies were cut from the longitudinal cross sections of melt-spun ribbons. The microstructures and different phases were examined by optical, scanning and transmission electron microscopy and the influence of the processing methods on microstructures of ribbons will be discussed