E. Lanzoni

“Tribological behaviour of multi-layered PVD nitride coatings”

Abstract Multi-layers resulting from the combination of layers of different PVD nitrides (TiN, Ti 2 N, Ti(C,N), (Ti,Al)N) were deposited by arc evaporation on AISI M2 tool steel and their tribological behaviour has been investigated. The effect of a MoS 2 layer deposited on top of the PVD nitride multi-layers was also studied. Dry sliding and abrasive wear behaviour have been studied by a slider-on-cylinder tribometer and a micro-scale abrasion tester, respectively. The main sliding wear mechanism was abrasion from hard particles formed at the contact interface as a consequence of extensive oxidation of the counter-material (hard chromium). The prevalence of abrasion damage in the sliding tests explains the good correlation between the results given by sliding tests at low applied loads and the micro-abrasion tests, and shows that hardness plays a key role in influencing the behaviour of the multi-layers. Milling tests, carried out in order to evaluate the cutting performance of coated tools, showed that end mills coated with the TiN-based multi-layers live longer than the others. The difference of performance was much less marked at the highest cutting speed.

Relationships among crystallographic structure, mechanical properties and tribological behaviour of electroless Ni–P(9%)/B4C films

Abstract The tribological behaviour of electroless Ni–P composite coatings was investigated by dry sliding tests with a slider-on-cylinder tribometer. The tests were carried out in laboratory air at room temperature against a PVD-TiN coated HSS cylinder. Friction and wear data are discussed on the basis of the mechanical properties (microhardness, plasticity parameter, fracture toughness) of the coatings, that were derived by indentation measurements at low loads. The wear depths measured on unreinforced Ni–P were about one order of magnitude larger than those obtained on the corresponding composite coatings. Furthermore, wear depth proved to increase with increasing annealing time, for both pure matrix and composite layers. The wear volume Q was correlated to the mechanical properties using Archard-type equations. For composite coatings the plasticity parameter δ H was inserted into the equation for the estimation of Q , in order to take into the account the action of a B 4 C-rich layer observed on the surface of the worn coatings.

Influence of composition on the thermal behaviour of chemically deposited nickel-phosphorus alloys

The thermal behaviour of a series of Ni-P alloys obtained by electroless plating from chloride-glycollate solutions at different pH values was studied by means of DSC analysis and X-ray diffraction.Alloys of composition up to Ni78P22 are microcrystalline or partially amorphous, depending on the P content; on heating up to 773 K, the amorphous phase is transformed into an equilibrium mixture of Ni and Ni3P crystals.Most of the alloys crystallize in two exothermic stages, these occurring ever closer to each other as the P concentration approaches the eutectic value; the alloys with near-eutectic compositions are the only ones crystallizing in one stage.The first thermal effect in hypo-eutectic alloys is due to the separation of Ni crystallites from the primary amorphous phase and/or to the growth of pre-existing solid-solution crystals; the second one is due to the crystallization of intermediate amorphous phase into Ni3P plus Ni. The first stage of crystallization in hyper-eutectic alloys corresponds to the formation of randomly-oriented Ni3P crystals, while in the second one the residual amorphous phase yields the eutectic mixture.ZusammenfassungDas thermische Verhalten einer Reihe von durch stromlose Platierung mit Chlorid-Clykollat-Lösungen bei verschiedenen pH-Werten erhaltenen Ni-P-Legierungen wurde mittels DSC und Röntgendiffraktion untersucht. Legierungen mit einer Zusammensetzung bis Ni78P22 sind abhängig vom P-Gehalt, kristallin oder teilweise amorph. Beim Erhitzen auf 773 K wird die amorphe Phase in ein Gleichgewichtsgemisch von Ni- und Ni3P-Kristallen überführt. Die meisten Legierungen kristallisieren in zwei exothermen Schritten, die sich einander umso mehr nähern, je mehr sich die P-Konzentration dem eutektischen Wert nähert. Als einzige kristallisieren die in der Zusammensetzung dem Eutektikum nahekommenden Legierungen in einem Schritt. Bei hypoeutektischen Legierungen ist der erste thermische Effekt der Ausscheidung von Ni-Kristallen aus der primären amorphen Phase und/oder dem Wachstum von bereits in der festen Lösung vorliegenden Kristallen, der zweite der Kristallization von Ni3P und Ni aus der intermediären amorphen Phase zuzuschreiben. Bei hypereutektischen Legierungen entspricht der erste Schritt der Kristallisation der Bildung von random-orientierten Ni3P-Kristallen, während des zweiten wird dagegen die verbleibende amorphe Phase in das eutektische Gemisch überführt.РезюмеС помощью ДСК и диффра кции рентгеновских лучей изучено термич еское поведение ряда Ni-P сплавов, получе нных безэлектродным никелированием из ра створов хлорид-гликолята при различных значениях pH. Сплавы с составом до Ni78P22 являют ся, в зависимости от соде ржания фосфора, микрокристаллическ ими или частично амор фными. При нагревании до 773 К а морфная фаза превращ ается в равновесную смесь Ni и Ni3P кристаллов. Большинство сплавов кристаллизуется в дв е экзотермические ста дии, которые сближаются по мере пр иближения концентра ции фосфора к эвтектическому зна чению. Сплавы с почти эвтект ическим составом кристаллизуются в од ну стадию. Первый терм ический еффект и гипо-эвтекти ческих сплавах обусл овлен разделением кристал литов никеля от первичной аморфно й фазы или же ростом кр исталлитов ранее существующего твердого раствора. Вт орой эффект обусловл ен кристаллизацией про межуточной аморфной фазы с образованием Ni3P и никеля. Первая стади я кристаллизации в гип ер-эвтектических сплавах соответству ет образованию произ вольно ориентированных кри сталлов Ni3P, тогда как на второй ст адии оставшаяся амор фная фаза дает эвтектическую с месь.

Tests on joints between steel and graphite

Abstract Under a research programme devoted to the study of metalceramic joints, which are of considerable importance in the field of advanced technology, various tests were performed on joining carbon steel to graphite by brazing with different filler metals. The results of each test are reported, with particular emphasis on the quality of the welded joint. The structural stability of the joints was also verified by long term annealing treatments at high temperature (850°C).