The aim of developing nanocrystalline and dispersion-strengthened titanium materials is to increase hardness and strength of titanium, thus improving the wear resistance of titanium implants. The dispersoids are used to prevent grain coarsening in the subsequent technologically necessary thermal treatment of nanocrystalline powder granulates as well as to increase hardness and strength of the titanium materials. Titanium silicides or titanium carbides, respectively, are chosen as dispersoids because silicon and carbon will scarcely have an adverse effect on the favourable TiO2 passive layer and will not affect the body tissue. The manufacture of titanium materials is carried out by high energy milling of Ti-Si/C powder blends. The compacting of the milled nanocrystalline powder granulates is done by means of spark plasma sintering a novel technique, by which the nanocrystalline microstructure is maintained by fast densification.

Wear-resistant titanium materials with high hardness and strength can be manufactured by introducing very fine titanium silicides and carbides into an ultrafine-grained titanium matrix. Nanocrystalline titanium particles with fine and homogeneous distributed carbon and silicon were generated by high energy ball milling of titanium with silicon powder or additions of the organic fluid hexamethyldisilane (HMDS). Spark Plasma Sintering (SPS) was chosen to compact the granules to prevent grain coarsening during sintering. Additionally, the Ti5Si3 and TiC x dispersoids limited grain coarsening. After sintering, the novel materials exhibited high hardness and strength, and excellent wear resistance. The electrochemical behaviour (comparable to that of commercially pure titanium) was also tested and showed the excellent suitability as an implant material.

Titanium materials with high strength and hardness at room temperature have been developed by introducing very fine Ti5Si3 dispersoids into an ultra-fine grained titanium matrix. After high-energy ball milling of a Ti–Si powder mixture SPS (spark plasma sintering) was used to consolidate the granules. For both process steps, an optimization of the parameters was necessary. XRD, SEM and TEM were used to investigate the mechanism of formation of Ti5Si3 dispersoids during SPS at various sintering temperatures and sintering times and furthermore, to characterize the microstructure with regards to titanium matrix grain size, dispersoid size and dispersoid distribution. The new material shows high hardness, strength and improved wear resistance in comparison to other titanium materials.

Dispersions of non-soluble ceramic particles in a metallic matrix can enhance the strength and heat resistance of materials. With the advent of mechanical alloying it became possible to put the theoretical concept into practice by incorporating very fine particles in a flirty uniform distribution into often oxidation- and corrosion- resistant metal matrices. e.g. superalloys. The present paper will give an overview about the mechanical alloying technique as a dry, high energy ball milling process for producing composite metal powders with a fine controlled microstructure. The common way is milling of a mixture of metallic and nonmetallic powders (e.g. oxides. carbides, nitrides, borides) in a high energy ball mill. The heavy mechanical deformation during milling causes also fracture of the ceramic particles to be distributed homogeneously by further milling. The mechanisms of the process are described. To obtain a homogeneous distribution of nano-sized dispersoids in a more ductile matrix (e.g. aluminium-or copper based alloys) a reaction milling is suitable. Dispersoid can be formed in a solid state reaction by introducing materials that react with the matrix either during milling or during a subsequent heat treatment. The pre-conditions for obtaining high quality materials, which require a homogeneous distribution of small dis-persoids, are: milling behaviour of the ductile phase (Al, Cu) will be improved by the additives (e.g. graphite), homogeneous introduction of the additives into the granules is possible and the additive reacts with the matrix or an alloying element to form hard particles that are inert with respect to the matrix also at elevated temperatures. The mechanism of the in-situ formation of dispersoids is described using copper-based alloys as an example. A comparison between the in-situ formation of dispersoids (TiC) in the copper matrix and the milling of Cu-TiC mixtures is given with respect to the microstructure and properties, obtained.

Strain and fracture mechanisms of Cu–TiC system with 5.3 vol % TiC was studied by an `in situ tensile test in SEM'. It was shown that during tensile strain the first cracks appear in the places with the largest strain after decohesion of larger particles or clusters of small particles from the matrix. A further stress increase causes the formation of `saw-like fracture' in an angle of 45° by interconnecting the rows of particles in the direction of tension. The fracture morphology is transcrystalline ductile. A model of fracture mechanism of the investigated system was suggested.

Copper alloys with high electrical and thermal conductivities in combination with high strength at elevated temperature have been developed by including very fine thermodynamically stable TiC dispersoids into a Cu or an age-hardenable CuTi4 matrix. TiC dispersion strengthened copper alloys were prepared by mechanical alloying in a planetary ball mill using a blend of atomized prealloyed CuTi(X) powder and graphite powder. The mechanism of the formation of TiC dispersoids during milling and heating at various temperatures was investigated using X-ray diffraction and by TEM investigations. The processing technique was found to result in TiC dispersoids of different sizes (diameter 10 to 50 nm) preferentially localized on the grain boundaries. The matrix of the alloys is microcrystalline (grain size 100 to 500 nm).The observed creep behaviour of the alloys is described in dependence on size and volume fraction of the dispersoids and the composition of the matrix. It is demonstrated that these alloys - despite their microcrystalline microstructure - show a high creep strength, provided numerous small dispersoids are located on the grain boundaries, thus effectively preventing grain boundary sliding.

In the paper a study of fracture mechanism of Cu-TiC system by an "in situ tensile test in SEM" was done, It is shown that during tensile strain the first cracks appear in the places with the largest critical strain epsilon = 0.16 after decohesion of larger particles or clusters of small particles. The further stress increase causes formation of a saw-like fracture in an angle alpha = 45 degrees following rows of particles declined from the direction of tension. The fracture morphology is transcrystalline ductile. A model of fracture mechanism in the investigated system was suggested.

TiC-dispersion-strengthened Cu alloys were prepared by mechanical alloying and subsequent hot extrusion. The evolution of the microstructure with respect to the preparation process is analysed by transmission electron microscopy techniques. The TiC dispersoids are formed in situ by the reaction of Ti and graphite. Ti diffuses from the pre-alloyed CuTi matrix to C inclusions which are embedded in the matrix after high-energy milling. Heat treatment of the powder mixtures at 400 degrees C leads to heterogeneous nucleation of TIC at the C/Cu interface. Thereby a well defined cube-on-cube orientation relationship is established between TiC and the Cu matrix. A study of the morphology of the TIC dispersoids shows that they are faceted on {111}(TiC), {110}(TiC) and {100}(TiC) planes and possess ledges on the atomic scale. The TiC/Cu interfaces are atomically abrupt and free of interface phases. The {100}(TiC)//{100}(Cu) and [110](TiC)//[110](Cu) topotaxy leads to a misfit of 17.6% between the adjacent lattices. This misfit is accommodated by a dislocation network along [100](Cu) directions.

Copper alloys with high electrical and thermal conductivities in combination with high elevated temperature strength can be developed, if finest thermodynamically stable TiC dispersoids are included into a copper matrix. For manufacturing TiC dispersion strengthened copper alloys, mechanical alloying was carried out in a planetary ball mill using a blend of atomized prealloyed CuTi(X) powder and graphite powder. Information on the mechanism of forming TiC dispersoids during milling and heating at various temperatures was obtained by using Xray diffraction and TEM investigations. Another way of manufacturing TiC dispersion strengthened copper alloys was to mill preformed, finely dispersed TiC powder (50nm) into pure copper powder. The two various processing techniques used made it possible to produce TiC dispersoids with different interface to the copper matrix. In addition, it was possible to change the microcrystalline microstructure of the dispersion strengthened alloys (100-300nm) into a coarse-grained microstructure (200-500 mu m) by heat treatment. The microstructure of these alloys is demonstrated by TEM and HRTEM investigations. The room temperature properties and the high temperature creep behavior of the alloys are described according to the different interfaces of the TiC dispersoids to the copper matrix, the position and the size of the TiC dispersoids and the grain size of the matrix.

High creep strength of dispersion strengthened alloys with microcrystalline grain size can be obtained if the dispersoids are very small and located mainly on the grain boundaries, thus preventing grain boundary sliding. For the creep investigations, TiC dispersion strengthened Cu alloys or Cu-Ti alloys made by mechanical alloying were used The processing technique used made it possible to produce TiC dispersoids of different sizes (10-50nm) formed by in-situ reactions and to localize them preferably an the grain boundaries. The matrix of the alloys is microcrystalline (100-500nm). The high temperature creep behavior of the alloys is described in terms of ifs dependence on size, position and volume fraction (3-10v/o) of the dispersoids. The microstructure of these alloys is demonstrated by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) investigations.