CP-Ti, Ti 6A l 4V (ELI), and Ti 6Al 7Nb are often used for manufacturing osteosynthesis products or implants. However, researches have revealed that Al and V can have detrimental effects on the human body. Therefore, several Al- and V-free near-α and (α+β) titanium alloys have been developed on the basis of CP-Ti Grade 4+ (Ti 0.4O 0.5Fe 0.08C). They should possess similar or better mechanical properties than Ti 6Al 4V (ELI) combined with an improved biocompatibility and good corrosion resistance. O, C, Fe, Au, Si, Nb, or Mo have been used as alloying elements, which are either already present in the human body or are biocompatible. Several of the studied alloys show a strength and ductility fulfilling the requirements of Ti 6Al 4V ELI as specified in ASTM F136. For instance, Ti 0.44O 0.5Fe 0.08C 2.0Mo exhibits a YTS of approx. 1005 MPa, an UTS of approx. 1015 MPa, and an elongation at rupture of at least 17%. Therefore, one or more of the studied alloys are promising candidates for replacing Ti 6Al 4V ELI in osteosynthesis and implant applications.

The hot corrosion Type II of the alloys FeCr20, FeCr20Ni10, FeCr20Ni20, and FeCr20Co10 is investigated at 700°C in air + 0.5% SO2 with deposits consisting of Na2SO4 and a eutectic mixture of Na2SO4 and MgSO4 for 24, 100, and 300 h. The alloying elements nickel and cobalt have a positive influence when tests are conducted using a MgSO4‐Na2SO4 deposit. In this case, they reduce the metal loss and increase the time to the propagation stage. In contrast, when the alloys are exposed with a Na2SO4 deposit, these alloying elements increase the metal loss and allow for the transition to the propagation stage because they can form molten phases with the Na2SO4. During the incubation stage an oxide scale forms on the FeCr20 alloy, which is thicker than the one formed during exposure without a deposit, and iron oxides are observed, which precipitate in the deposit. The propagation stage occurs by a dissolution and precipitation mechanism forming localized pitting attack. Iron is the main species that dissolves and precipitates, while chromium remains mainly as an oxide beneath the initial surface. The additional elements are found in the pit and in the salt deposit.

The type II hot corrosion behavior of the alloys NiCr20, NiCr20Co10, and NiCr20Fe10 is investigated at 700°C in synthetic air + 0.5% SO2 for up to 300 hr. Pure Na2SO4 and a eutectic mixture of MgSO4–Na2SO4 are applied as deposits. The kinetics are investigated via dimensional metrology and correlated to the microstructural progression of the corrosion by examining the cross‐sections. All alloys exhibit two‐stage corrosion kinetics, with initially low and subsequently increased metal losses. Independent of the deposit composition, the metal loss after the longest exposure time is increased by the alloying element cobalt, whereas it is decreased for the iron‐containing alloy. All alloys show increased metal losses when exposed to the MgSO4–Na2SO4 deposit. The time to the propagation stage is similar for all tests. During the stage of low metal loss, all alloys develop a chromia scale and internal chromium sulfides. When the propagation stage is reached, chromium and nickel can be found along with oxygen and sulfur within the pit. Nickel is dissolved into the deposit, where it precipitates.

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With the goal of increasing the combustion temperature and decreasing the weight of todays aero engines, the application of SiC/SiC ceramic matrix composites is widely investigated and first parts are in service. Besides the many advantages of SiC/SiC ceramic matrix composites, some challenges are encountered and have to be overcome to ensure a reliable operation. One of these challenges is the protection of the ceramic matrix composites from oxidation and volatilization. The oxidation of silicon carbide results in the formation of silicon dioxide, which is generally considered protective. The combustion atmosphere, however, contains water vapor and other contaminations. The water vapor results in the formation of volatile silicon hydroxide, while contaminations, like CMAS or Na2SO4, can result in spallation or an increase in oxidation rates. Also, the fiber matrix interface coatings are more prone to oxidation and need to be protected to avoid loss in mechanical properties. Therefore, a coatings system, consisting of an outer environmental barrier coating and an inner bond coat, is applied to SiC/SiC ceramic matrix composite when used in turbine engines. Within this study alternative bond coats are developed mainly based on aluminum oxide formers, which are in itself less prone to volatilization at the designated temperature of 1200°C. The coating process is realized via chemical vapor deposition, which can coat complex parts cost effectively and without the need for a line-of-sight. The coatings provide a reservoir of the oxide forming species and therefore the oxide scale is able to heal upon crack formation or spallation. One of the developed coatings is based on an oriented aluminum nitride layer, which is in contrast to bulk AlN resistant to high temperature oxidation in humid air. The influence of the orientation and the chlorine content, which is present due to the coating procedure, on the increased oxidation resistance is investigated. Cyclic exposures are done to investigated spallation and cracking behavior due to mismatches in thermal expansion. Further, the resistance to hot corrosion type I is compared to other materials used or investigated for the hottest sections of turbine engines. The microstructure of the coatings was examined before and after the exposures using X-ray diffraction, scanning electron microscopy and electron beam microanalysis.