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Microstructure and mechanical properties of TiC/Ti matrix composites and Ti–48Al–2Cr–2Nb alloy joints brazed with Ti–28Ni eutectic filler alloy

Dong Duo, Xu Haitao, Zhu Dongdong, Wang Gang, He Qing, Lin Junpin

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1259--1267

EN

Ti–48Al–2Cr–2Nb and TiC/Ti matrix composites were successfully joined using Ti–28Ni eutectic filler metal at different brazing temperatures. Microstructure and mechanical properties of the joints were systematically studied. The results showed that the joints all showed integral interfaces and the microstructures of the joints for 980 8C/15 min were detected as Ti-48Al-2Cr-2Nb/a2-Ti3Al + t3-Al3NiTi2/a2-Ti3Al/Ti(s,s) + d-Ti2Ni + TiC/Ti matrix composites. As brazing temperature increased, continuous Ti2Ni layer diminish and Ti2Ni phase became more discrete. However, a2-Ti3Al rich layer has thickened which deteriorates the properties of the joints. The highest shear strength achieved 469.5 MPa as the joint brazed at 1010 8C for 15 min. The evolution of microstructures brazed with different tem-peratures was studied and its relationship with the shear strength was also revealed in details.

2

Analysis on the mixed friction between the guide made of cast iron and the valve stem made of Ti6Al4V with and without protective layer

Kuchar M., Siczek K.

Archiwum Motoryzacji

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2014

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Vol. 64, nr 2

37--47, 137--147

EN

Lightweight valves are commonly used in modern combustion engines with cam and camless valve train. They can be made of TiAl alloys and in particular the inlet valves can be made of TJ6AI4V. The stems of such valves can be coated by protective layer obtained by nitridation, chroming or the other one. The stems can mate with guides made of cast iron, of phosphor bronze or berylium bronze. Mating can take place in conditions of mixed friction with different share of lubricated friction. The researches have been provided in the tribotester. The analyzed valve has been driven electromagnetically, for the different valve strokes and frequencies. The mating takes place in the condition of oil absence. The valve has been loaded by additional mass to induce the normal force between valve stem and its guide. It has been measured the acceleration and the displacement of the valve, the impact force of the valve into its seat insert, friction force between valve stem and its guide and the sound level. The aim of the researches is to obtain and compare values and courses of friction coefficient between the guide made of cast iron and valve stem made of Ti6Al4V for certain number of the valve strokes and frequencies. The researched stem could be uncoated or coated by Cr layer or by nitridation. The analytical model has been elaborated to calculate the contact pressure and the friction force between valve stem and its guide for the conditions of mixed friction occurring for the selected engine oil and the valve motion relative to its guide as obtained from the tribotester. The obtained dry friction coefficient values have been used in the model. Results of researches have been presented in the article.

PL

Zawory lekkie są powszechnie stosowane w nowoczesnych silnikach spalinowych z rozrządami krzywkowymi i bezkrzywkowymi. Mogą one być wykonane ze stopów TiAl, a w szczególności zawory dolotowe mogą być wykonane z Ti6AI4V. Trzonki takich zaworów mogą być powlekane warstwą ochronną otrzymaną przez chromowanie, azotowanie lub inną. Trzonki zaworów mogą współpracować z prowadnicami wykonanymi z żeliwa, brązu fosforowego lub berylowego. Współpraca może odbywać się w warunkach tarcia mieszanego ze zmiennym udziałem tarcia płynnego. Badania zostały przeprowadzone na tribotesterze. Analizowany zawór był napędzany elektromagnetycznie, dla różnych skoków i częstotliwości. Współpraca odbywała się w warunkach braku smarowania. Zawór został obciążony przez dodatkową masę do wywołania normalnej siły między trzonkiem zaworu i jego prowadnicą. Mierzono przyspieszenie i przemieszczenie zaworu, siłę uderzenia zaworu o jego gniazdo, siłę tarcia pomiędzy trzonkiem zaworu i jego prowadnicą oraz poziom hałasu. Celem tych badań jest uzyskanie i porównywanie wartości i przebiegów współczynnika tarcia między prowadnicą wykonaną z żeliwa i trzonkiem zaworu z Ti6AI4V dla pewnej liczby skoków zaworu i częstotliwości. Badany trzonek mógł być niepowlekany lub powlekany warstwą chromu bądź azotowany. W celu obliczenia nacisku i siły tarcia pomiędzy trzpieniem zaworu i jego prowadnicą w warunkach tarcia mieszanego występującego dla wybranego oleju silnikowego i takiego ruchu zaworu względem jego prowadnicy, jaki występował w tribotesterze, został opracowany model analityczny. W modelu zostały wykorzystane uzyskane wartości współczynnika tarcia suchego. Wyniki badań zostały przedstawione w artykule.

3

Researches on friction force between valve made of tial and its guide made of phosphorous bronze

Siczek K.

Journal of KONES

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2013

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Vol. 20, No. 1

295--301

EN

A lightweight valve can be one made of steel but with a drilled stem. Another one can be made of TiAl alloys and its stem can be full or drilled. Lightweight valve can be also ceramic one made of Si3N4. Such valves can mate with guides made of cast iron or of phosphorous bronze in varying conditions in their common contact zone. The aim of researches has been to measure friction force in contact zone between valve stem made of TiAl alloy and its guide made of phosphorous bronze, in the absence of oil. The conditions of room temperature and of the atmosphere pressure have been used during experiment. Mentioned researches have been provided in tester, which design has been presented in the article. The loading of contact zone has varied periodically during serie. The displacement and acceleration of valve and the force during its impact into seat insert have been measured during tests. Additionally the sound level has been measured, either. Tests have been provided for different frequency of driving force. Obtained results of researches has been shown in the article. In all cases the measured sound level have been equal 94 dBA, when sound level of laboratory environment has been equal 40 dBA. Values for coefficient of friction between valve stem and its guide can change from 0.12 to 0.16 and decrease almost linearly with increasing of loading frequency. Values of dry friction coefficient between valve stem made of TiAl alloy and coated by chrome and its guide made of phosphorous bronze can be smaller up to 17% than values obtained in case of valve stem coated by nc-WC/a-C:H mating with a guide made of cast iron.

4

The researches on the friction properties of nc-WC/a-C : H coating on the lightweight valve stem

Siczek K.

Journal of KONES

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2012

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Vol. 19, No. 2

493-500

EN

The lightweight valves, especially made of TiAl alloys, are more and more often used in modern combustion engines with cam and camless valvetrain. To increase the wear resistance and to decrease the coefficient of friction between valve steam and valve guide, different kinds of the coating are used. The researched valve has been outlet one made of TiAl6Zr4Sn2Mo2 alloy with the original chrome coating on the valve stem. The nc-WC/a-C:H nanocoating has been deposited on the chromed stem of researched valve, which has mated with the guide made of cast iron. The aim of the present paper is to investigate friction properties of such nc-WC/a-C:H deposited onto the chromed and polished surface of the valve stem. The scheme of research stand has been presented in the paper. On the stand it has been possible to measure values of valve lift and of valve acceleration, the impact force between valve and its seat insert, the friction force between valve stem and its guide, the temperature values for valve guide and for seat insert and a sound level during impacting. Researches have been performed in conditions of room temperature and without oil lubrication in the valve stem - guide contact zone. Basing on the measured values of friction force between valve stem and its guide vs. time and loading frequency, the coefficient of friction has been estimated. Obtained curves of friction force and of friction coefficient vs. time, for different frequency values of valve loading have been presented in the article.