Which academic masterpiece did Zhu Xi complete in 4 years?

You mean the Outline of Zi Zhi Tong Jian, also known as the Outline of Ziyang, but this book was not finalized before Zhu Xi's death. It was edited by Zhao Shiyuan, his protege, in Fan Chuan College after Zhu Xi's death, and was written in Song Xiaozong Road for eight years (1172).

Zhu Xi had many well-known works before his death. He bootstrapped himself as a scholar until his death. In every 5 years, he experienced four dynasties: Gaozong, Xiaozong, Guangzong and Ningzong. He was an official for nine years, and he stood in the dynasty for forty days, teaching "University" for Ningzong. The other forty years lived a life of giving lectures and writing books. His works include the original meaning of Zhouyi, Enlightenment, Textual Research on Gua Gua, Biography of Poetry, Doctrine of the Mean in Universities, Four Books or Questions, Notes on Analects of Confucius, Notes on Mencius, Explaining Taiji Pictures, Explaining All Books, Explaining Ximing and Collected Songs of Chu. In addition, there are 1 volumes of Collected Works, 11 volumes of Sequel, 1 volumes of Bieji, and 14 volumes of Zhuziyu compiled by worshippers. His Yi-ology thoughts are mainly concentrated in the original meaning of Zhouyi, Enlightenment of Yi-ology, Zhuzi Genre and other books. According to Zhu Xi's Chronology, The Original Meaning of Zhouyi was written in the fourth year of Chunxi (AD 1177), and Enlightenment was written in the thirteenth year of Chunxi (AD 1186).