"conversation expanded" is correct and usable in written English.
You can use it to describe a situation in which a conversation has grown to include more and more people. For example, "The conversation expanded to include five new people as the night went on."
Before long, the conversation expanded into disgust for the entire political climate.
Kaufman: "So how long would something like this take Joan Mitchell to paint?" Dean Lorich, Tristan's dad: "When critics look at a new painting, what are they thinking?" Soon, the conversation expanded to encompass other artistic pursuits.
In short order, the group's membership soared and the conversation expanded to include the full promise of the page's name, as members, in a kind of collective therapy, began reflecting on every part of their high school experience: teachers, the high-pressure academic curriculum, the general challenges of adolescence.
As Andrew grew older, the conversation expanded to the broader subject of American history, politics and World War II.
An amazing cast, including Jeff Goldblum, Vincent Kartheiser, Kumail Nanjiani, and a fuming Giamatti, begins by rating Amy's looks, but as the conversation expands the men begin to fight about the roots of sexual attraction, the rise of female comedy, and just whose tastes count as normal.
It was the mayor who commanded the conversation, expanding on topics that were agreeable to him, like the stories his mother told him about patriotism during World War I and his several visits to Puerto Rico's capital, San Juan, where, he said, there was a fortress with "cannons".
David Clifford Burger, an attorney with Robinson Brog Leinwand Greene Genovese & Gluck representing the Abramson institute, said that "I can't in a telephone conversation expand on the factual allegations in the complaint".
I look forward to that kind of conversation expanding more.
"The conversation expands in really interesting ways once we get T Bone involved in it," Joel Coen said.
These conversations expanded outside of the chessboard in London.
The conversations expanded our horizons and reassured us that we can have a diverse movement given partners with such big hearts.
