Structural transformations in the solid state dictate operating regimes of materials for engineering applications. Advanced structural characterisation facilitated by electron microscopy has resulted in significant progress in our understanding of structural transformations across resolvable length scales. We shall confine this communication to one of the metallic systems. This refers to titanium (Ti) alloys. They exhibit formation of a variety of solid solution phases, intermetallic phases, quasicrystals, incommensurate structures, and metallic glasses under different processing conditions. Additionally, newer phase formation at nanometer length scales has also been observed in Ti alloys. The exploration of properties in presence of structures at nanoscale in these alloys have not been discussed in literature extensively. Such an approach will open an avenue for nano-engineered alloys. An attempt will be made to indicate the direction of investigation in this connection succinctly. Understanding the nature and pathways of solid state structural transformations in Ti alloys seem to be important in view of the wide variety of engineering applications. Nanostructured materials have shown formation of newer phases not included in equilibrium phase diagrams. This review shall dwell on this aspect by drawing parallelism from many other alloy systems at nanoscale. In particular, $\mathrm{Au}-\text{Cu}$ nanostructures will be discussed as an example. It will be argued that size of the system will have influence on the formation of structures that are normally not observed at microscopic length scales in Ti alloys. In view of the complexities involved in phase transformations in Ti alloys, it is important to evolve or look for a model that will help us understand structural transformations by minimum geometrical distortion from a parent phase. Such an approach will offer one of the ways of comprehending formation of phases at nanoscale. In addition to this, it will also help us to consider group-subgroup relationship. It will be shown that unified structural description towards this will be helpful. A brief summary of higher dimensional structural modelling will be presented here with particular reference to phases formed in Ti alloys.

固态的结构转变决定了工程应用材料的操作方式。电子显微镜促进的先进结构表征使我们对跨可分辨长度尺度的结构转变的理解取得了重大进展。我们将把这种通信限制在一个金属系统中。这是指钛（Ti）合金。它们在不同的加工条件下表现出各种固溶体相、金属间相、准晶、不相称结构和金属玻璃的形成。此外，在钛合金中还观察到纳米长度尺度的新相形成。文献中尚未广泛讨论这些合金中纳米级结构存在下的性能探索。这种方法将为纳米工程合金开辟一条道路。将尝试简洁地表明这方面的调查方向。鉴于广泛的工程应用，了解钛合金固态结构转变的性质和途径似乎很重要。纳米结构材料已显示出未包含在平衡相图中的新相的形成。本综述将通过与许多其他纳米级合金系统进行比较来重点讨论这一方面。尤其，$\mathrm{金}-\text{铜}$将以纳米结构为例进行讨论。有人认为，系统的尺寸会对钛合金中通常在微观长度尺度上观察不到的结构的形成产生影响。鉴于钛合金相变的复杂性，发展或寻找一种模型非常重要，该模型将帮助我们通过母相的最小几何变形来理解结构转变。这种方法将提供一种理解纳米级相形成的方法。除此之外，它还有助于我们考虑组与子组的关系。将会表明，对此的统一结构描述将是有帮助的。这里将特别参考钛合金中形成的相，对高维结构模型进行简要总结。